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DAC IV stages
Yahzi
post Feb 20 2013, 18:38
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How important are DAC IV stages in the design of a DAC? I've heard they can cause audible differences. Is this true? I'm not a DAC designer, but I assume there are those who understand the technical merits. Is it a big deal?
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John_Siau
post Feb 20 2013, 22:52
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Take a look at published specifications for D/A converters, DVD players, sound cards, iPod, etc. Many only have an 80 to 90 dB SNR. This means that the noise will be audible in an A/B/X test if the peak music levels exceed 80 to 90 dB SPL (easily achieved).

Worse yet, most D/A converters are preceded by a digital volume control. If 20 dB of digital attenuation is dialed in (very typical), the SNR will degrade by 20 dB. In many systems, the user will need to apply 20 dB of digital attenuation to achieve a playback level that peaks at 100 dB SPL. Under these conditions the converter noise may reach 30 to 40 dB SPL. It is not hard to hear the noise floor drop from 30 of 40 dB SPL to less than 0 dB SPL in an A/B/X test.

I have an ABX tester, and it is very easy to pick out D/A converters that have high noise floors.

If one wishes to use a digital volume control, the D/A converter will need an extra 20 dB SNR to keep noise inaudible at loud playback levels. If we want to achieve "CD" quality and use 20 dB of digital attenuation, then 116 dB SNR is required. Under these conditions, noise may still become audible if playback peaks exceed 96 dB SPL.

D/A converters with >116 dB SNR are few and far between. Noise alone is a dead giveaway when comparing D/A converters.

This post has been edited by John_Siau: Feb 20 2013, 22:57


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saratoga
post Feb 20 2013, 23:51
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QUOTE (John_Siau @ Feb 20 2013, 16:52) *
Take a look at published specifications for D/A converters, DVD players, sound cards, iPod, etc. Many only have an 80 to 90 dB SNR.


You're exaggerating. Most quality players (iPods included) are very nearly quantization noise limited over line out. 80dB is quite rare and would be exceptionally bad for a name brand device. The Apple stuff will give you 15.5 effecitve bits over headphone out with full analog volume control for not all that much money.

QUOTE (John_Siau @ Feb 20 2013, 16:52) *
D/A converters with >116 dB SNR are few and far between. Noise alone is a dead giveaway when comparing D/A converters.


Yeah but in reality it doesn't make much difference since you never use that dynamic range. CDs using > 80dB dynamic range are far rarer then D/A converters with < 80dB dynamic range.
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John_Siau
post Feb 21 2013, 14:57
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QUOTE (saratoga @ Feb 20 2013, 17:51) *
80dB is quite rare and would be exceptionally bad for a name brand device. The Apple stuff will give you 15.5 effecitve bits over headphone out with full analog volume control for not all that much money.


15.5 effective bits when the volume control is set at maximum, and to the best of my knowledge, none of the Apple devices have analog volume control (please correct me if I am wrong). With 20 dB digital attenuation, 15.5 effective bits becomes 12.2 effective bits. The problem is that significant amounts of digital attenuation are often used at normal listening levels, and the converter noise is often audible.

QUOTE (saratoga @ Feb 20 2013, 17:51) *
Yeah but in reality it doesn't make much difference since you never use that dynamic range. CDs using > 80dB dynamic range are far rarer then D/A converters with < 80dB dynamic range.


CD and high-resolution low-noise recordings do exist, and if these are used in an ABX test, the noise floors of many converters should be audible (on the basis of calculated SPL of the noise).


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saratoga
post Feb 21 2013, 20:00
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QUOTE (John_Siau @ Feb 21 2013, 08:57) *
QUOTE (saratoga @ Feb 20 2013, 17:51) *
80dB is quite rare and would be exceptionally bad for a name brand device. The Apple stuff will give you 15.5 effecitve bits over headphone out with full analog volume control for not all that much money.


15.5 effective bits when the volume control is set at maximum, and to the best of my knowledge, none of the Apple devices have analog volume control (please correct me if I am wrong).


All portable electronics have analog volume control, Apple's included. You couldn't buy an mp3 player that had digital volume control if you wanted to. They aren't made.

QUOTE (John_Siau @ Feb 21 2013, 08:57) *
With 20 dB digital attenuation, 15.5 effective bits becomes 12.2 effective bits. The problem is that significant amounts of digital attenuation are often used at normal listening levels, and the converter noise is often audible.


Yeah but no one does this so it doesn't matter.

Edit: Although I don't mean to imply that analog volume control imposes no SNR hit. I'm sure at the lowest volume the SNR on an ipod is much worse. But at reasonable volumes its more then sufficient, which is what I was trying to say.

QUOTE (John_Siau @ Feb 21 2013, 08:57) *
QUOTE (saratoga @ Feb 20 2013, 17:51) *
Yeah but in reality it doesn't make much difference since you never use that dynamic range. CDs using > 80dB dynamic range are far rarer then D/A converters with < 80dB dynamic range.


CD and high-resolution low-noise recordings do exist, and if these are used in an ABX test, the noise floors of many converters should be audible (on the basis of calculated SPL of the noise).


Yes, but people don't buy CE to do ABX tests of specially selected samples. They buy them to listen to music. With enough effort I can find samples that break MP3, AAC, Vorbis, etc. Doesn't mean I dislike those formats. It just means I can break them if I try.

This post has been edited by saratoga: Feb 21 2013, 20:11
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John_Siau
post Feb 21 2013, 23:03
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QUOTE (saratoga @ Feb 21 2013, 14:00) *
All portable electronics have analog volume control, Apple's included. You couldn't buy an mp3 player that had digital volume control if you wanted to. They aren't made.


Absolutely incorrect!

Almost all of these products all have buttons or cap-touch buttons (or sliders) that control volume up and down. In almost all cases, the volume control is a digital multiplier. Very few consumer products still have analog volume controls (variable resistors) in the audio path. DSP is cheap and is already required to do MP3 decoding.


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saratoga
post Feb 21 2013, 23:23
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QUOTE (John_Siau @ Feb 21 2013, 17:03) *
QUOTE (saratoga @ Feb 21 2013, 14:00) *
All portable electronics have analog volume control, Apple's included. You couldn't buy an mp3 player that had digital volume control if you wanted to. They aren't made.


Absolutely incorrect!


Name one such product. Just one.

QUOTE (John_Siau @ Feb 21 2013, 17:03) *
Almost all of these products all have buttons or cap-touch buttons (or sliders) that control volume up and down. In almost all cases, the volume control is a digital multiplier.


You've obviously never reverse engineered any of these devices if you think this.

Edit: I mean think about what you're claiming. Any modern device can set the line out and headphone out volume independently. Do you really think theres two stereo DACs included just so that they can use independent digital volume adjustments? No, that'd be nuts, the cost would be huge. They have independent volume control because the headphone amp and line out amp volume is software controlled.

This post has been edited by saratoga: Feb 21 2013, 23:36
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John_Siau
post Feb 22 2013, 15:15
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QUOTE (saratoga @ Feb 21 2013, 17:23) *
QUOTE (John_Siau @ Feb 21 2013, 17:03) *
QUOTE (saratoga @ Feb 21 2013, 14:00) *
All portable electronics have analog volume control, Apple's included. You couldn't buy an mp3 player that had digital volume control if you wanted to. They aren't made.


Absolutely incorrect!


Name one such product. Just one.

QUOTE (John_Siau @ Feb 21 2013, 17:03) *
Almost all of these products all have buttons or cap-touch buttons (or sliders) that control volume up and down. In almost all cases, the volume control is a digital multiplier.


You've obviously never reverse engineered any of these devices if you think this.

Edit: I mean think about what you're claiming. Any modern device can set the line out and headphone out volume independently. Do you really think theres two stereo DACs included just so that they can use independent digital volume adjustments? No, that'd be nuts, the cost would be huge. They have independent volume control because the headphone amp and line out amp volume is software controlled.

Wrong, but your conclusion that two DACs would be required is correct!

The Apple devices use Cirrus CLI158881 Stereo Codecs which are similar to the CS42L73. These devices have two stereo DACs, one stereo ADC, and a digital mixing engine. Such chips form the audio core of almost all portable devices. Digital gain control is ubiquitous.

See:

http://www.cirrus.com/en/products/cs42l73.html

This post has been edited by John_Siau: Feb 22 2013, 15:16


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Arnold B. Kruege...
post Feb 22 2013, 16:33
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QUOTE (John_Siau @ Feb 22 2013, 09:15) *
QUOTE (saratoga @ Feb 21 2013, 17:23) *

QUOTE (John_Siau @ Feb 21 2013, 17:03) *

QUOTE (saratoga @ Feb 21 2013, 14:00) *

All portable electronics have analog volume control, Apple's included. You couldn't buy an mp3 player that had digital volume control if you wanted to. They aren't made.


Absolutely incorrect!


Name one such product. Just one.


The Apple devices use Cirrus CLI158881 Stereo Codecs which are similar to the CS42L73. These devices have two stereo DACs, one stereo ADC, and a digital mixing engine. Such chips form the audio core of almost all portable devices. Digital gain control is ubiquitous.

See:

http://www.cirrus.com/en/products/cs42l73.html


Agreed. The usual chips we find in mainstream portable digital audio player and smart phones and tablets generally has at last 4 DACs and 2 ADCs. Even though they are not all used by the specific products, this is also true of the SOC that is the heart of the economically-priced Sansa Clip+ and Fuze.
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saratoga
post Feb 22 2013, 17:58
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QUOTE (scuttle @ Feb 22 2013, 09:49) *
From NWAVGuy's dissection and review of the Clip:

http://nwavguy.blogspot.co.uk/2011/02/sans...p-measured.html

DAC linearity is important because most portable devices have digital volume controls that reduce the signal before the DAC


ha, hes wrong. I somehow missed that reading the review.

QUOTE (scuttle @ Feb 22 2013, 09:49) *
And I'm new here and have never taken a DAP apart, but requiring that someone you disagree with undertake the entire burden of proof while you should be assumed correct by default seems a bit much.


How exactly do I prove that something doesn't exist? I can point out that I've worked on drivers for lots of these devices and not one of them uses digital gain control, but I can't really prove it since I haven't worked on every single device in existence, just a lot of them.

QUOTE (Arnold B. Krueger @ Feb 22 2013, 10:33) *
Agreed. The usual chips we find in mainstream portable digital audio player and smart phones and tablets generally has at last 4 DACs and 2 ADCs. Even though they are not all used by the specific products, this is also true of the SOC that is the heart of the economically-priced Sansa Clip+ and Fuze.


No, those are 1 stereo DAC devices. Two is actually rare in low power devices, and off hand I can't think of any dedicated MP3 players that do that. I think that Cirrus part above is aimed more at tablets and higher power devices, so probably they can afford a little more logic.
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scuttle
post Feb 22 2013, 19:01
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QUOTE (saratoga @ Feb 22 2013, 16:58) *
QUOTE (scuttle @ Feb 22 2013, 09:49) *
From NWAVGuy's dissection and review of the Clip:

http://nwavguy.blogspot.co.uk/2011/02/sans...p-measured.html

DAC linearity is important because most portable devices have digital volume controls that reduce the signal before the DAC


ha, hes wrong. I somehow missed that reading the review.



No. You have failed to understand your own post. You wrote:

You couldn't buy an mp3 player that had digital volume control if you wanted to. They aren't made.


That the chip used in the Clip (assuming this is your evidence for your contention - you didn't bother saying why anybody should listen to you) has analog AND digital volume control still makes NWAVguy right and you wrong. Read what you wrote!

And if that chip isn't your evidence, then what is? Are people supposed to say "Yes; this man is angry and can't use apostrophes - clearly he must be in the right!"? No.



QUOTE
QUOTE (scuttle @ Feb 22 2013, 09:49) *
And I'm new here and have never taken a DAP apart, but requiring that someone you disagree with undertake the entire burden of proof while you should be assumed correct by default seems a bit much.


How exactly do I prove that something doesn't exist? I can point out that I've worked on drivers for lots of these devices and not one of them uses digital gain control, but I can't really prove it since I haven't worked on every single device in existence, just a lot of them.


Yes: your claim was inherently unprovable - which makes it silly - but if you could name a couple of major players then that would at least be indicative.

And you can claim to have written drivers, but so what? The Internet is full of people who claim to be special forces, CIA agents, and aliens - especially when they think it will help them win some silly debate. NWAVGuy is a reasonable expert witness because everyone here knows that he is competent enough to design the ODAC; all we know about you is that you can type.
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saratoga
post Feb 22 2013, 19:39
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QUOTE (scuttle @ Feb 22 2013, 13:01) *
No. You have failed to understand your own post. You wrote:

You couldn't buy an mp3 player that had digital volume control if you wanted to. They aren't made.


The Clip does not have digital volume control, so even if you take that statement hyper-literally, its still correct (although its also not what I meant).

QUOTE (scuttle @ Feb 22 2013, 13:01) *
That the chip used in the Clip (assuming this is your evidence for your contention - you didn't bother saying why anybody should listen to you) has analog AND digital volume control still makes NWAVguy right and you wrong. Read what you wrote!

And if that chip isn't your evidence, then what is? Are people supposed to say "Yes; this man is angry and can't use apostrophes - clearly he must be in the right!"? No.


Well I wrote the volume control code used in that review, and its open source, so you can read it if you want:

http://git.rockbox.org/?p=rockbox.git;a=co...81ad204720e0eb0


QUOTE (scuttle @ Feb 22 2013, 13:01) *
Yes: your claim was inherently unprovable - which makes it silly - but if you could name a couple of major players then that would at least be indicative.


I don't follow you. Why is pointing out that Apple, Sandisk and virtually all other companies use analog volume control unprovable or silly?

QUOTE (scuttle @ Feb 22 2013, 13:01) *
And you can claim to have written drivers, but so what? The Internet is full of people who claim to be special forces, CIA agents, and aliens - especially when they think it will help them win some silly debate. NWAVGuy is a reasonable expert witness because everyone here knows that he is competent enough to design the ODAC; all we know about you is that you can type.


You can easily google my username and verify that I've written this stuff. Or just search on these forums. I post about this stuff a lot, and plenty of people here know me, NWAVguy included.
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John_Siau
post Feb 22 2013, 20:13
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QUOTE (saratoga @ Feb 22 2013, 13:39) *
Well I wrote the volume control code used in that review, and its open source, so you can read it if you want:

http://git.rockbox.org/?p=rockbox.git;a=co...81ad204720e0eb0


Rockbox uses the MAS3539F MP3 decoder and Codec.

This chip has only one D/A and one A/D as Saratoga has been claiming.

One block diagram (page 7 of the data sheet) shows a volume control feature in the headphone amplifier (following the D/A converter). This implies that the unit has some analog volume control capability.

However, a more detailed block diagram on page 8 shows digital mixing and audio processing before the D/A converter (in the digital domain).

The truth is that the MAS3539F uses both analog and digital volume control. The following is a quote from page 10 of the data sheet:

"To minimize quantization noise, the main volume control
is automatically split into a digital and an analog
part. The volume range is −114...+12 dB with an additional
mute position. A balance function is provided."

Register 00 11 controls the main volume. This is "split
between a digital and an analog function" (see page 51 of the data sheet).

Bottom line, some MP3 players may use a combination of analog and digital gain control (see MAS3539F) . Others only use digital gain control (see CS42L73).


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saratoga
post Feb 22 2013, 20:36
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QUOTE (John_Siau @ Feb 22 2013, 14:13) *
Bottom line, some MP3 players may use a combination of analog and digital gain control (see MAS3539F) .


Like I said above, modern devices do have digital mixers. So what? However, the MAS isn't a modern device. Its a 1990s hardware MP3 decoder with no CPU. It dates back to a time when mobile CPUs were too slow to process audio. If you're really going to try and argue this, do you want to pick something from at least this millenium smile.gif

QUOTE (John_Siau @ Feb 22 2013, 14:13) *
Others only use digital gain control (see CS42L73).


Did you see above where I showed that this is not true?

Like I said before, you're just wrong about "almost all" of these devices using software volume control. I've never seen a portable device that uses software volume control, and apparently you have not either. Or if you have, feel free to tell me about it . . .
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John_Siau
post Feb 22 2013, 20:46
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QUOTE (saratoga @ Feb 22 2013, 14:36) *
Like I said before, you're just wrong about "almost all" of these devices using software volume control. I've never seen a portable device that uses software volume control, and apparently you have not either. Or if you have, feel free to tell me about it . . .


A digital volume control can be implemented in hardware or software. It is often implemented in hardware and the software merely sends register commands to the hardware (as in the Rockbox). Rockbox code exists for MAS3539F hardware, and this is why I used this chip as an example. I assumed your code was written to support this chip. Did you write code for a different chip? If so, which one(s). What chip is used in the clip?


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saratoga
post Feb 22 2013, 20:53
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QUOTE (John_Siau @ Feb 22 2013, 14:46) *
QUOTE (saratoga @ Feb 22 2013, 14:36) *
Like I said before, you're just wrong about "almost all" of these devices using software volume control. I've never seen a portable device that uses software volume control, and apparently you have not either. Or if you have, feel free to tell me about it . . .


A digital volume control can be implemented in hardware or software. It is often implemented in hardware and the software merely sends register commands to the hardware (as in the Rockbox). Rockbox code exists for MAS3539F hardware, and this is why I used this chip as an example. I assumed your code was written to support this chip. Did you write code for a different chip? If so, which one(s). What chip is used in the clip?


Rockbox is an operating system that runs on many dozens of different devices each with different DACs. The MAS is the first device it ever ran on, being the hardware decoder of one of the very first MP3 players ever made. But you misunderstand the meaning of those registers. The MAS does not provide software access to it's PCM data. There are hardware registers for scaling data because its impossible to do it any other way, and scaling data is often needed (for example, volume normalization). Volume control is supposed to be implemented using a variable gain amplifier (and in fact we do implement it this way).

There are many different clip players. The first used the AS3525 which had a DAC similar to the AS3514 integrated. The newer ones (that are being discussed here) use an unknown chip dubbed (by us) the AS3525v2, which uses a DAC that is related to the AS3543 (although the register maps are not quite identical).

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John_Siau
post Feb 22 2013, 21:13
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QUOTE (saratoga @ Feb 22 2013, 14:53) *
Rockbox is an operating system that runs on many dozens of different devices each with different DACs. The MAS is the first device it ever ran on, being the hardware decoder of one of the very first MP3 players ever made. But you misunderstand the meaning of those registers. The MAS does not provide software access to it's PCM data. There are hardware registers for scaling data because its impossible to do it any other way, and scaling data is often needed (for example, volume normalization). Volume control is supposed to be implemented using a variable gain amplifier (and in fact we do implement it this way).

There are many different clip players. The first used the AS3525 which had a DAC similar to the AS3514 integrated. The newer ones (that are being discussed here) use an unknown chip dubbed (by us) the AS3525v2, which uses a DAC that is related to the AS3543 (although the register maps are not quite identical).


I fully understand the purpose of the registers in the MAS, and I understand that the MAS does not give the CPU access to the PCM data. But, digital "scaling" is digital volume control. It may not be the primary volume control system, but it still performs part of the volume control function. 6 dB of gain reduction via "scaling" will move the audio 6 dB closer to the noise floor. This digital scaling can also cause truncation if it is not dithered.

A variable gain amplifier may also attenuate the audio without having much impact on the output noise.

In either case, if the signal is decreased without also decreasing the output noise, then the effective SNR is reduced.

An analog pot (not found on many modern devices) has the ability to reduce the signal and the noise simultaneously (thus preserving the SNR of the audio). Digital volume controls and variable gain amplifiers do not replicate the function of a true analog gain control.


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saratoga
post Feb 22 2013, 21:38
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QUOTE (John_Siau @ Feb 22 2013, 15:13) *
QUOTE (saratoga @ Feb 22 2013, 14:53) *
Rockbox is an operating system that runs on many dozens of different devices each with different DACs. The MAS is the first device it ever ran on, being the hardware decoder of one of the very first MP3 players ever made. But you misunderstand the meaning of those registers. The MAS does not provide software access to it's PCM data. There are hardware registers for scaling data because its impossible to do it any other way, and scaling data is often needed (for example, volume normalization). Volume control is supposed to be implemented using a variable gain amplifier (and in fact we do implement it this way).

There are many different clip players. The first used the AS3525 which had a DAC similar to the AS3514 integrated. The newer ones (that are being discussed here) use an unknown chip dubbed (by us) the AS3525v2, which uses a DAC that is related to the AS3543 (although the register maps are not quite identical).


I fully understand the purpose of the registers in the MAS, and I understand that the MAS does not give the CPU access to the PCM data. But, digital "scaling" is digital volume control. It may not be the primary volume control system, but it still performs part of the volume control function. 6 dB of gain reduction via "scaling" will move the audio 6 dB closer to the noise floor. This digital scaling can also cause truncation if it is not dithered.


You're mixing up truncation and scaling. Truncation (with or without dithering) happens no matter what. All of these devices operate at 32 bit internally (except truly ancient devices like the MAS). You always truncate your 32 bit PCM coming out of your MP3/FLAC/whatever decoder down to 16 bit (or 24 bit in the case of PCs). Note that this happens no matter how volume control is implemented. So its no surprise you see the signs of that under a scope. A quality 16 bit device should basically be expected to do that since dithering is uncommon.

Now you can also scale the waveform. In rockbox we do this too, although only by small amounts (a few dB for EQ precut, replaygain, etc). This doesn't change the situation with truncation, since that still has to happen. Finally, at the end you have volume control, which is done by changing gain to preserve SNR.


QUOTE (John_Siau @ Feb 22 2013, 15:13) *
A variable gain amplifier may also attenuate the audio without having much impact on the output noise.

In either case, if the signal is decreased without also decreasing the output noise, then the effective SNR is reduced.

An analog pot (not found on many modern devices) has the ability to reduce the signal and the noise simultaneously (thus preserving the SNR of the audio). Digital volume controls and variable gain amplifiers do not replicate the function of a true analog gain control.


Yes of course. Like I said before:

QUOTE
However, while they'll all give you nearly 16 bit limited performance into a line out, they tend to have fairly limited amplifiers (ignoring Apple, Sandisk which are very good). They also have essentially fixed noise floors that are independent of volume. So a more useful approach is to think about them in terms of the impedance and sensitivity that will give good performance. The noise floor puts a limit on sensitivity, since very high sensitivity headphones will produce more acoustic noise, while the finite output impedance limits how low of an impedance can be driven without distortion.


The fixed noise floor kills you. So while analog gain is better then digital, it doesn't save you running into the noise floor at low volumes. So SNR does decrease, although slower then 6dB/bit of digital. The flip side of this though is that going to more effective bits doesn't really help you (unless you do it by reducing the device's analog noise floor). My point, therefore, was that since we operate under these constraints at all but the very highend, worrying about DAC design is not very productive. You need better analog amplifiers after the DAC or its all for nothing.
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John_Siau
post Feb 22 2013, 22:21
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QUOTE (saratoga @ Feb 22 2013, 15:38) *
The fixed noise floor kills you. So while analog gain is better then digital, it doesn't save you running into the noise floor at low volumes. So SNR does decrease, although slower then 6dB/bit of digital. The flip side of this though is that going to more effective bits doesn't really help you (unless you do it by reducing the device's analog noise floor). My point, therefore, was that since we operate under these constraints at all but the very highend, worrying about DAC design is not very productive. You need better analog amplifiers after the DAC or its all for nothing.

I agree, and yes amplifiers are sometimes a limiting factor.

If digital gain control is used, the quality of the converter must increase to maintain the same level of performance that could be achieved with an analog gain control following the converter. Every 6.02 dB of gain reduction that is used in normal listening will require 1 additional bit of effective resolution. If we start with 129 dB SNR (as in the DAC2), then we can use generous amounts of digital volume control without impacting the overall performance of our playback system (the power amplifier almost always becomes the limiting factor). But if we start with a laptop that has a 95 dB SNR and use the digital volume control on iTunes or Windows Media Player or the OS then the situation is very different. iTunes and WMP do not control the gain of an amplifier following the internal DAC, they control the gain in software (digital gain control). These players and most other computer audio applications place significant demands upon the performance of the built-in DACs. In a typical media server system, (line out to amplifier, or headphone jack to headphones) the overall performance will suffer if significant use of the software volume control is necessary to achieve a normal listening level. You can't start with a 95 dB DAC and apply 20 dB attenuation and expect 16-bit performance. In a practical system, few users want to operate at 100% volume to reach a normal listening level (even though this would give the best SNR). The sensitivity of the amplifier or headphones demand that adjustments are made.

Many users are perfectly satisfied with the resulting (95-20)=75 dB effective SNR. However, it is not unreasonable to expect that people will notice a difference when connecting a 129 dB converter to the laptop media server and amplifier. The differences should be detectable in ABX tests. I posted ABX test results showing the effects of truncation (different issue), but similar tests could and should be run on consumer products operating at typical volume settings.

This post has been edited by John_Siau: Feb 22 2013, 22:22


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John Siau
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saratoga
post Feb 22 2013, 22:24
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QUOTE (John_Siau @ Feb 22 2013, 16:21) *
But if we start with a laptop that has a 95 dB SNR and use the digital volume control on iTunes or Windows Media Player or the OS then the situation is very different. iTunes and WMP do not control the gain of an amplifier following the internal DAC, they control the gain in software (digital gain control).


Is that actually true? Seems like such a dumb design choice I doubt it, but I don't know much about how the guts of Windows work.

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John_Siau
post Feb 22 2013, 22:38
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QUOTE (saratoga @ Feb 22 2013, 16:24) *
QUOTE (John_Siau @ Feb 22 2013, 16:21) *
But if we start with a laptop that has a 95 dB SNR and use the digital volume control on iTunes or Windows Media Player or the OS then the situation is very different. iTunes and WMP do not control the gain of an amplifier following the internal DAC, they control the gain in software (digital gain control).


Is that actually true? Seems like such a dumb design choice I doubt it, but I don't know much about how the guts of Windows work.

Yes, the gain control is software-based DSP.

Software-based digital gain control is easy to implement on a fast processor. A stereo gain-control function places almost no load on the CPU.

From our discussion, it looks like some MP3 players have attempted to do things a little differently, but I am not sure the results are much different (due to the noise limitations of the variable gain amplifiers). If noise does not change when the volume control is adjusted, then the results are nearly identical (in terms of effective SNR).


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saratoga
post Feb 23 2013, 04:02
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QUOTE (Arnold B. Krueger @ Feb 22 2013, 17:01) *
QUOTE

If thats true, then I suppose I was right to be skeptical about the above claims given that the ALC888 has analog volume control.


The block diagram of the ALC 888 can be found in Figure 1, page 3 of ftp://209.222.7.36/pc/audio/ALC861_DataSheet_1.3.pdf

I read it as saying that only the analog inputs of the ALC 888 have an analog volume control. It appears to me that the path from the DAC to its output terminal ha no analog volume control. Only muting (off/on analog swtich) seems to be shown.


I can't use that link, but it says "ALC861". Using this link:

http://www.hardwaresecrets.com/datasheets/...taSheet_1.1.pdf

The ALC861 does have analog volume control.

Looking at this link:

http://www.hardwaresecrets.com/datasheets/ALC888_1-0.pdf

There is a viable gain amp for the ALC888.

I think digital gain control is very uncommon for PCs as well. The intel AC97 spec called for analog control. I believe the newer HD audio spec does as well.

I'm less familiar with PCs though.

QUOTE ( @ Feb 22 2013, 16:38) *
QUOTE (saratoga @ Feb 22 2013, 16:24) *
QUOTE (John_Siau @ Feb 22 2013, 16:21) *
But if we start with a laptop that has a 95 dB SNR and use the digital volume control on iTunes or Windows Media Player or the OS then the situation is very different. iTunes and WMP do not control the gain of an amplifier following the internal DAC, they control the gain in software (digital gain control).


Is that actually true? Seems like such a dumb design choice I doubt it, but I don't know much about how the guts of Windows work.

Yes, the gain control is software-based DSP.

Software-based digital gain control is easy to implement on a fast processor. A stereo gain-control function places almost no load on the CPU.


Yes but it puts a lot of strain on the DAC by reducing the SNR for no reason at all. It would be very simple to implement a more intelligent mixer that simply scaled the analog volume to maximize SNR. Do you have some documentation indicating that MS or Apple chose not to implement such an obvious feature?


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Posts in this topic
- Yahzi   DAC IV stages   Feb 20 2013, 18:38
- - John_Siau   The I-V (current to voltage) conversion stage of a...   Feb 20 2013, 20:48
|- - Soap   QUOTE (John_Siau @ Feb 20 2013, 14:48) Fo...   Feb 21 2013, 03:37
|- - John_Siau   QUOTE (Soap @ Feb 20 2013, 21:37) QUOTE (...   Feb 21 2013, 15:20
|- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 21 2013, 09:20) QU...   Feb 21 2013, 16:09
- - Yahzi   Thanks for the reply John. I'm getting a few p...   Feb 20 2013, 21:47
- - John_Siau   Designing an I-V converter with a 130 dB SNR is no...   Feb 20 2013, 22:02
|- - Yahzi   But it is largely irrelevant if it is competently ...   Feb 20 2013, 22:28
||- - benski   QUOTE (Yahzi @ Feb 20 2013, 16:28) But it...   Feb 20 2013, 22:44
|- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 20 2013, 16:02) De...   Feb 21 2013, 16:11
|- - John_Siau   QUOTE (Arnold B. Krueger @ Feb 21 2013, 10...   Feb 21 2013, 16:47
- - John_Siau   Take a look at published specifications for D/A co...   Feb 20 2013, 22:52
|- - saratoga   QUOTE (John_Siau @ Feb 20 2013, 16:52) Ta...   Feb 20 2013, 23:51
||- - John_Siau   QUOTE (saratoga @ Feb 20 2013, 17:51) 80d...   Feb 21 2013, 14:57
||- - saratoga   QUOTE (John_Siau @ Feb 21 2013, 08:57) QU...   Feb 21 2013, 20:00
||- - John_Siau   QUOTE (saratoga @ Feb 21 2013, 14:00) All...   Feb 21 2013, 23:03
||- - saratoga   QUOTE (John_Siau @ Feb 21 2013, 17:03) QU...   Feb 21 2013, 23:23
|||- - John_Siau   QUOTE (saratoga @ Feb 21 2013, 17:23) QUO...   Feb 22 2013, 15:15
||||- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 22 2013, 09:15) QU...   Feb 22 2013, 16:33
|||||- - saratoga   QUOTE (scuttle @ Feb 22 2013, 09:49) From...   Feb 22 2013, 17:58
|||||- - scuttle   QUOTE (saratoga @ Feb 22 2013, 16:58) QUO...   Feb 22 2013, 19:01
|||||- - saratoga   QUOTE (scuttle @ Feb 22 2013, 13:01) No. ...   Feb 22 2013, 19:39
||||||- - John_Siau   QUOTE (saratoga @ Feb 22 2013, 13:39) Wel...   Feb 22 2013, 20:13
||||||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 14:13) Bo...   Feb 22 2013, 20:36
||||||- - John_Siau   QUOTE (saratoga @ Feb 22 2013, 14:36) Lik...   Feb 22 2013, 20:46
||||||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 14:46) QU...   Feb 22 2013, 20:53
||||||- - John_Siau   QUOTE (saratoga @ Feb 22 2013, 14:53) Roc...   Feb 22 2013, 21:13
||||||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 15:13) QU...   Feb 22 2013, 21:38
|||||||- - John_Siau   QUOTE (saratoga @ Feb 22 2013, 15:38) The...   Feb 22 2013, 22:21
|||||||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 16:21) Bu...   Feb 22 2013, 22:24
|||||||- - John_Siau   QUOTE (saratoga @ Feb 22 2013, 16:24) QUO...   Feb 22 2013, 22:38
|||||||- - greynol   QUOTE (John_Siau @ Feb 22 2013, 13:38) So...   Feb 22 2013, 22:48
||||||||- - John_Siau   QUOTE (greynol @ Feb 22 2013, 16:48) Is t...   Feb 22 2013, 22:57
||||||||- - greynol   QUOTE (John_Siau @ Feb 22 2013, 13:57) Ye...   Feb 22 2013, 23:05
|||||||- - saratoga   QUOTE (Arnold B. Krueger @ Feb 22 2013, 17...   Feb 23 2013, 04:02
|||||||- - Arnold B. Krueger   QUOTE (saratoga @ Feb 22 2013, 22:02) Loo...   Feb 23 2013, 17:11
|||||||- - John_Siau   QUOTE (Arnold B. Krueger @ Feb 23 2013, 11...   Feb 27 2013, 15:10
|||||||- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 27 2013, 09:10) In...   Feb 27 2013, 16:30
||||||||- - John_Siau   QUOTE (Arnold B. Krueger @ Feb 27 2013, 10...   Mar 4 2013, 17:28
||||||||- - Soap   QUOTE (John_Siau @ Mar 4 2013, 11:28) QUO...   Mar 5 2013, 01:11
|||||||- - Nessuno   QUOTE (John_Siau @ Feb 27 2013, 15:10) Wh...   Feb 28 2013, 13:57
||||||- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 22 2013, 15:13) An...   Feb 22 2013, 22:56
||||||- - John_Siau   QUOTE (Arnold B. Krueger @ Feb 22 2013, 16...   Feb 22 2013, 23:06
|||||- - greynol   QUOTE (scuttle @ Feb 22 2013, 10:01) That...   Feb 22 2013, 19:42
|||||- - Arnold B. Krueger   QUOTE (greynol @ Feb 22 2013, 13:42) QUOT...   Feb 22 2013, 20:36
|||||- - greynol   QUOTE (Arnold B. Krueger @ Feb 22 2013, 11...   Feb 22 2013, 20:43
||||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 09:15) Wr...   Feb 22 2013, 17:48
|||- - scuttle   QUOTE (saratoga @ Feb 21 2013, 22:23) QUO...   Feb 22 2013, 15:49
||- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 21 2013, 17:03) QU...   Feb 22 2013, 16:10
||- - John_Siau   QUOTE (Arnold B. Krueger @ Feb 22 2013, 10...   Feb 22 2013, 19:41
|- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 20 2013, 16:52) Ta...   Feb 21 2013, 16:00
||- - John_Siau   QUOTE (John_Siau @ Feb 20 2013, 16:52) Ta...   Feb 21 2013, 18:44
|||- - [JAZ]   QUOTE (John_Siau @ Feb 21 2013, 18:44) sy...   Feb 21 2013, 20:36
|||- - John_Siau   QUOTE ([JAZ] @ Feb 21 2013, 14:36...   Feb 21 2013, 22:49
|||- - [JAZ]   That the usual listening volume of most electronic...   Feb 21 2013, 23:45
|||- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 21 2013, 16:49) QU...   Feb 22 2013, 16:27
|||- - John_Siau   QUOTE (Arnold B. Krueger @ Feb 22 2013, 10...   Feb 22 2013, 18:17
|||- - John_Siau   The following quote from NwAvGuy's Sansa Clip+...   Feb 22 2013, 18:32
|||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 12:17) In...   Feb 22 2013, 18:40
||||- - John_Siau   QUOTE (saratoga @ Feb 22 2013, 12:40) I...   Feb 22 2013, 19:10
||||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 13:10) QU...   Feb 22 2013, 19:45
||||- - John_Siau   QUOTE (saratoga @ Feb 22 2013, 13:45) I d...   Feb 22 2013, 20:38
||||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 14:38) QU...   Feb 22 2013, 20:42
|||- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 22 2013, 12:17) Bu...   Feb 22 2013, 20:58
|||- - saratoga   QUOTE (Arnold B. Krueger @ Feb 22 2013, 14...   Feb 22 2013, 21:07
|||- - Arnold B. Krueger   QUOTE (saratoga @ Feb 22 2013, 15:07) QUO...   Feb 22 2013, 23:01
||- - Ethan Winer   QUOTE (Arnold B. Krueger @ Feb 21 2013, 10...   Feb 21 2013, 20:43
|- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 20 2013, 16:52) D/...   Feb 21 2013, 16:04
|- - John_Siau   QUOTE (Arnold B. Krueger @ Feb 21 2013, 10...   Feb 21 2013, 16:28
|- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 21 2013, 10:28) QU...   Feb 21 2013, 18:28
- - Yahzi   So your view is that it is a potential issue but i...   Feb 20 2013, 23:09
- - saratoga   I think SNR is probably not the best way to think ...   Feb 22 2013, 00:05
- - greynol   Since when has NwAvGuy been the ultimate arbiter o...   Feb 22 2013, 18:53
|- - scuttle   QUOTE (greynol @ Feb 22 2013, 17:53) Sinc...   Feb 22 2013, 19:08
|- - greynol   QUOTE (scuttle @ Feb 22 2013, 10:08) You...   Feb 22 2013, 19:18
- - greynol   So rockbox uses the analog volume control, which i...   Feb 22 2013, 20:27
- - greynol   1) 6 dB is not 20 dB 2) Downward scaling in order...   Feb 22 2013, 21:30
- - Mach-X   Rather ironic that everybody is rather correct. Th...   Mar 5 2013, 11:47


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