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DSD vs PCM, bit vs hz, Is there a way to compare them fairly?
Arnold B. Kruege...
post Feb 13 2014, 14:00
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QUOTE (Wombat @ Feb 12 2014, 20:09) *
Shouldn't the tube amp adding more own distortion by design as any modern DAc should?


Just because its made with tubes doesn't mean that it is necessarily audibly flawed.

But yes it is hard to make a tubed buffer that doesn't add measurable noise and distortion to the output of a good DAC.

But on balance there's the slight matter of the source at one end, and the transducer at the other and they are generally the weakest link.

Finally, the well known limitations of human hearing at its best which it often is not, is generally the ultimate limiting factor.

QUOTE
How can someone rate the source at all with a tube amp behind, leave alone assigning it to PCM, DSD or filtering?


Some call it naivete, some call it arrogance, and some call it wishful thinking. ;-)


QUOTE
Did i simply get the test setup wrong?


Probably you were too kind to it! ;-)
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AstralStorm
post Feb 13 2014, 23:01
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Homemade passive switchbox with a good toggle button and connectors. No monkey business there, low capacitance.
Switchbox is after the DACs - it's not a coax spdif switchbox.

The amp has low harmonic distortion, espectially higher up - but that isn't an issue with DACs anyway.
What might be problematic for DACs is the relatively low input impedance, on the order of 50 kOhm.
--

Yeah, I'd love to blind test everything. Pity it takes a bunch of hours. Note that every switcheroo took me a bunch of minutes to discern and be sure. It's that slight a difference.
Plus the switcher is only two port. I also have not tested any other inputs than coax SPDIF.


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mzil
post Feb 13 2014, 23:52
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QUOTE (mzil @ Feb 12 2014, 08:46) *
Did you have to hand this switchbox back to your assistant (helper) each time...

I'm still looking for an answer to this part of my question. Thanks.
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AstralStorm
post Feb 14 2014, 00:01
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QUOTE (mzil @ Feb 13 2014, 23:52) *
QUOTE (mzil @ Feb 12 2014, 08:46) *
Did you have to hand this switchbox back to your assistant (helper) each time...

I'm still looking for an answer to this part of my question. Thanks.


No, the coax cables were long enough. I didn't even listen while they were being reconnected. The devices were in another room. The DACs were given a bunch of minutes (~2 minutes at least, likely more, I didn't measure) to sync properly. Cables were ~3m long. (But cable length doesn't worsen jitter and is neglible for the connection to the amp at audio frequencies.)

This post has been edited by AstralStorm: Feb 14 2014, 00:03


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mzil
post Feb 14 2014, 00:14
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Thanks.

Another question: What was the channel tracking error value of the dual-ganged analog potentiometer used to level match the Presonus FP10 to the other DAC?
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AstralStorm
post Feb 14 2014, 00:19
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QUOTE (mzil @ Feb 14 2014, 00:14) *
Thanks.

Another question: What was the channel tracking error value of the dual-ganged analog potentiometer used to level match the Presonus FP10 to the other DAC?


The actual pot balance is irrelevant - it is a digital volume control actually. At the position involved the outputs were balanced properly in both devices according to the voltmeter. (Which is 0.05% error at the range. I could use better hardware.)

Both devices were ran with "standard" -6 dB and not 0 dB. (I like my digital volume controls done in software, but this test used a better SPDIF interface which does not have a volume control. (loaner Audiophileo 2) I wanted to exclude USB/Firewire handling from influencing this test, as well as reduce the effect of SPDIF jitter if any.)

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mzil
post Feb 14 2014, 01:12
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I've never heard of a digital rotary volume knob which when noisy or scratchy can be remedied by a squirt of contact cleaner, as this FP10 owner attests fixed his volume problem:
http://forum.recordingreview.com/f9/scratc...nus-fp10-42612/

Also a different reviewer (Chris from DE, dated 01/16/13) from another site complains of his newer Presonus unit, "The only problem I have is sometimes the main volume pot gets noisy when turning", here:
http://www.musiciansfriend.com/pro-audio/p...rding-interface
but his solution is the old rotate the pot back and forth to scrape the contacts clean method: "...after a few rolls, it is clean".

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Wombat
post Feb 14 2014, 01:45
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QUOTE (AstralStorm @ Feb 12 2014, 05:49) *
However, I'd say that excellent R2R DACs (say, old AKM or TI PCM series) are better than some otherwise excellent sigma-delta DACs (such as Cirrus Logic, Wolfson or ESS; sigma-delta AKM is indistinguishable to me from R2R). The difference is minor, but there and ABXable.
PCM is the base format for an R2R DAC, DSD is the base format for a sigma-delta DAC.
So, not all DACs are sigma-delta. Heck, for cost-no-object purposes you can make an R2R DAC at home, given precision resistors.

Most DACs which support both, handle them equally well - but there are few exceptions - mostly using ESS chips. Again, the difference is minor.
(On an unrelated note: ESS Sabre blows, it's tonally off somehow.)

Excuse me but even if this ABX experiment has some kind of logic i really have a problem with nearly all stated conclusions here and how you prove that.
This is why we have a TOS that tries to prevent some talk about tender feelings being attributed to different kind of gear.
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AstralStorm
post Feb 14 2014, 07:39
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I do know about the TOS. Talking about "tender feelings" when I cannot name why it sounds different seems fine to me.
That's why I called it something nebulous like "timbre". If I was able to say "one of those sounds like it has less jitter" or "one of these has overshoot, the other does not" then I would, but I do not know what actually causes the audible difference.
I've excluded a few obvious items such as frequency response and noise floor (covered by amp).
It is possible that the 0.5% difference in loudness is actually audible - both of the devices were around 40 sons, since that's how loud I listen - think radio broadcast at decent not too loud volume.
Both use high line out levels in consumer range, so there is likely an amplifier in the way.
Note that in case of FP10, said amplifier is different than the one in mic/line ins apparently. (Those are not linear in FR!)
It is also possible that chiptunes cause an audible difference in IMD - they have lots of high frequency contents and square waves.

mzil: I used the back line outs in FP10 - they still have a volume control, but it is digital. Fancy design, same pot controls both digital and analog volume depending on the output in question. I know specifically because the low levels do not cause channel imbalance like with phones out.
The tracking of the pot is important when you're controlling the mic/line ins, main out or phones out. (And the tracking capability is so-so, but in this range it is good - near the center of the pot for -6 dB.)
Lynx Hilo has a digital control only on line outs as well.

--
Next time I'll do a double-blind trial, but without the loaner converter... But not any time soon.

On the topic, I've quick tested DSD64 vs PCM (24bit, 44.1k) on my Lynx Hilo. Failed to notice any difference in ABX at 16 long trials. This is "reportedly" not true with some chipsets, specifically said ESS Sabre 9018.

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mzil
post Feb 14 2014, 08:39
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QUOTE (AstralStorm @ Feb 12 2014, 05:26) *
Volume was matched using a voltmeter on 1kHz sine to within 0.5% - the knobs on FP10 didn't allow a better match.

Using the FP10's knobs to control the level matching, as you wrote in that post, means you were using an analog potentiometer. This applies not just to the MAIN OUT knob (and the PHONES OUT knob); the MIX knob also works in the analog domain.
From Presonus FP10 User Manual:

"Mix. The mix knob is like a balance control. It balances the headphone MAIN and CUE outputs between
Inputs 1-8 and playback outputs 1 and 2. This feature is an analog hardware mixer..."

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AstralStorm
post Feb 14 2014, 08:41
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Hmm. Regardless, I have checked and the tracking was way better than volume matching.

Do you recommend I should run a test with DACs on a bench connected to a linear power supply, driven by I2S off an ARM microcomputer?
This could be arranged, but I have much more important things to do for a long time.

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mzil
post Feb 14 2014, 08:45
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QUOTE (AstralStorm @ Feb 13 2014, 23:39) *
mzil: I used the back line outs in FP10 - they still have a volume control, but it is digital. Fancy design, same pot controls both digital and analog volume depending on the output in question. I know specifically because the low levels do not cause channel imbalance like with phones out.

That doesn't prove anything. They are separate knobs and all your observation supports is that the PHONES OUT analog pot happens to seem inferior in regards to low level channel tracking, at least on your sample unit. Another person with the same unit might happen to get a better headphone pot, or worse.
---

I personally feel outboard DAC testing is almost worthless. Even in nearly ideal, double-blind, well controlled conditions, people inevitably hear differences [if they do at all] due to the various electronics, including the op amps used in these units, not the actual DAC chips themselves. Small impedance mis-matches from the output device to the switcher/preamp causing subtle frequency responses errors and channel tracking error causing small lateral shifts in the soundstage also come into play at times, even if the listeners aren't conscious of it and attribute the changes to other things.

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AstralStorm
post Feb 14 2014, 13:35
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Oh, but what if the difference is in the chip itself too? I'm not sure anyone has tried it.
I'd also like to test opamps double blind some time later - both as a buffer and with gain 4, at +/- 12V from a linear power supply.
The same breadboard setup could do both. The tricky part is randomly switching between the devices - I'll need a good passive crosspoint switch (or a multitarget DPDT) for that.

Hmm, actually, cable-or could work too, as opamps have a huge output impedance anyway.
Not sure if the same applies to cable-or of DACs - they have low enough impedance for that to possibly matter - but it is a constant condition.

If you think an impedance mismatch of way less than 0.1 Ohm is audible (also picofarad order of capacitance mismatch), I'd say you're a proponent of cable audibility and you really should try to ABX that. As I said, I've actually measured the voltages to within 0.5%. Including the switcher in all 4 configurations of cables.

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Arnold B. Kruege...
post Feb 14 2014, 14:04
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QUOTE (mzil @ Feb 14 2014, 02:45) *
I personally feel outboard DAC testing is almost worthless. Even in nearly ideal, double-blind, well controlled conditions, people inevitably hear differences [if they do at all] due to the various electronics, including the op amps used in these units, not the actual DAC chips themselves. Small impedance mis-matches from the output device to the switcher/preamp causing subtle frequency responses errors and channel tracking error causing small lateral shifts in the soundstage also come into play at times, even if the listeners aren't conscious of it and attribute the changes to other things.


Anybody who thinks good op amps have sonic signatures needs to ABX about 20 of them cascaded - and get thoroughly humiliated.

ADCs and DACs are among the most perfected of all audio components, but op amps can be even better on the test bench.

Preserving +/- 0.1 dB matching across an entire audio system is doable - generally only good level matching is required.

As far as the metering goes - +/- 0.1 dB is about the same as +/- 1%. Flat response in the meter is not an absolute requirement because the goal is matching, not necessarily flat response.

The Uni-T UT61E 5 digit DVM is a reasonably priced tool for this job, and it is very flat over the audio band and beyond.

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AstralStorm
post Feb 14 2014, 14:47
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I wouldn't be so sure about "inaudible" - IMD behavior differences could in theory be audible, especially on complex signals. (Products on the order of -40 dB exist.)
It does not cascade trivially either. The difference, if any, would be very subtle though.

Remember what you're asking for though: 10 high end audio opamps costs some $100 and you'd need more than one brand... You're asking someone to toss $400 + more in precision resistors and capacitors.
Loopback testing would necessarily involve additional DAC/ADCs which could make the test invalid. I happen to have a bunch of spare ADA4898-1s, but that makes only for 5 pairs.
I also have a slightly cheaper Uni-T meter, 3,5 digits.

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Arnold B. Kruege...
post Feb 14 2014, 16:01
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QUOTE (AstralStorm @ Feb 14 2014, 08:47) *
I wouldn't be so sure about "inaudible" - IMD behavior differences could in theory be audible, especially on complex signals. (Products on the order of -40 dB exist.)
It does not cascade trivially either. The difference, if any, would be very subtle though.


Spurious responses on the order of -40 dB in the normal audible range from a good op amP? Please provide a real world example.

QUOTE
Remember what you're asking for though: 10 high end audio opamps costs some $100


I said nothing about high end op amps. I said good op amps. The tests I was party to involved TL074s.

QUOTE
and you'd need more than one brand...


No, this is not an attempt to prove a global truth. Besides, if 20 TL074 sections are transparent, why would you need more expensive chips?


QUOTE
You're asking someone to toss $400 + more in precision resistors and capacitors.


Test was done with standard grade generic parts, which are actually quite sonically transparent. The test can be done with only resistors in the signal path, and good 1% parts can now be had for pennies each.

QUOTE
Loopback testing would necessarily involve additional DAC/ADCs which could make the test invalid.


This is a discussion about op amps only. But converters are not that much harder. Most of my tests involved converters in pro grade audio interfaces.

QUOTE
I happen to have a bunch of spare ADA4898-1s, but that makes only for 5 pairs.
I also have a slightly cheaper Uni-T meter, 3,5 digits.



I see much more complexity than is actually necessary. If one actually does good ABX test one tends to find that the latest-greatest higher end stuff is unecessary.

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mzil
post Feb 14 2014, 18:20
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QUOTE (Arnold B. Krueger @ Feb 14 2014, 06:04) *
QUOTE (mzil @ Feb 14 2014, 02:45) *
I personally feel outboard DAC testing is almost worthless. Even in nearly ideal, double-blind, well controlled conditions, people inevitably hear differences [if they do at all] due to the various electronics, including the op amps used in these units, not the actual DAC chips themselves. Small impedance mis-matches from the output device to the switcher/preamp causing subtle frequency responses errors and channel tracking error causing small lateral shifts in the soundstage also come into play at times, even if the listeners aren't conscious of it and attribute the changes to other things.

Anybody who thinks good op amps have sonic signatures...

That wasn't my point, at all.
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AstralStorm
post Feb 14 2014, 21:56
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QUOTE (Arnold B. Krueger @ Feb 14 2014, 16:01) *
QUOTE (AstralStorm @ Feb 14 2014, 08:47) *
I wouldn't be so sure about "inaudible" - IMD behavior differences could in theory be audible, especially on complex signals. (Products on the order of -40 dB exist.)
It does not cascade trivially either. The difference, if any, would be very subtle though.


Spurious responses on the order of -40 dB in the normal audible range from a good op amP? Please provide a real world example.


Ok, I'll provide a graph, it's not a standard IMD test, uses more tones. (a large chord)
Standard two tone CCIF IMD can be easily -60 dB on good parts. In a great implementation, -80 dB.
That with expensive AD8610s. TL074 is way worse at it.

The resistors don't need to be 0.1%, yes, but they have to be paired. Plus you need a good listen with hard tracks. (again, chiptunes, noise and metal are best IMO)
Anyway, this is off-topic. Where's the on-topic thread?

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Arnold B. Kruege...
post Feb 15 2014, 18:49
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QUOTE (AstralStorm @ Feb 14 2014, 15:56) *
QUOTE (Arnold B. Krueger @ Feb 14 2014, 16:01) *
QUOTE (AstralStorm @ Feb 14 2014, 08:47) *
I wouldn't be so sure about "inaudible" - IMD behavior differences could in theory be audible, especially on complex signals. (Products on the order of -40 dB exist.)
It does not cascade trivially either. The difference, if any, would be very subtle though.


Spurious responses on the order of -40 dB in the normal audible range from a good op amP? Please provide a real world example.


Ok, I'll provide a graph, it's not a standard IMD test, uses more tones. (a large chord)
Standard two tone CCIF IMD can be easily -60 dB on good parts. In a great implementation, -80 dB.
That with expensive AD8610s. TL074 is way worse at it.

The resistors don't need to be 0.1%, yes, but they have to be paired. Plus you need a good listen with hard tracks. (again, chiptunes, noise and metal are best IMO)
Anyway, this is off-topic. Where's the on-topic thread?


How about this for a multitone?



This tone's peak amplitude is -1 dB FS It was looped from the output to the input of a popular-priced M-Audio 1010LT 8 channel in, 8 channel out audio interface which uses <$0.50 NE5532 op amp chips for buffers.

http://www.jameco.com/webapp/wcs/stores/se...CFUhp7AodxmMAUA

All spurious responses appear to be > 115 dB down, which assures total inaudibility.

Note this is not a high end or premium audio interface and is built with standard commercial grade parts. There are at least 2 op amp buffers, a DAC and an mid-grade ADC in the loop.

http://www.m-audio.com/images/global/manua...10LT-Manual.pdf

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Wombat
post Feb 15 2014, 21:55
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Arnold you miss the point. You have to do a good listen on hard tracks!
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Arnold B. Kruege...
post Feb 16 2014, 13:26
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QUOTE (Wombat @ Feb 15 2014, 15:55) *
Arnold you miss the point. You have to do a good listen on hard tracks!


If you put a smiley on that I'd be laughing, but in the absence of any evidence of attempted humor I must deal with the above as a criticism.

I suggest that you reread the post I was responding to. It made a specific technical claim involving a measurement which I addressed.

There is also a bit of background to this. In another thread I strongly supported the idea that at this point in the current SOTA we must use listening tests to evaluate very complex audio tools such as perceptual coders.

This is not true of simple electronic devices such as op amps, power amps, ADCs, DACs and even loudspeakers. Since they perform relatively simple forms of signal processing and other than loudspeakers generally perform orders of magnitude better than our hearing thresholds, relatively simple technical tests are very applicable. This fact is represented in widely accepted recommendations for technical gear used for doing critical listening tests such as BS 1116-1. Please see section 7 "Reproduction devices".
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Wombat
post Feb 16 2014, 14:13
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QUOTE (Arnold B. Krueger @ Feb 16 2014, 13:26) *
If you put a smiley on that I'd be laughing, but in the absence of any evidence of attempted humor I must deal with the above as a criticism.

I thought it is that obvious i don't need a smiley.
AstralStorm does some statements here all the time that sound exactly like the audiophile nonsense posted elsewhere and when asking for evidence the next statement follows again with no solid evidence. "you need a good listen with hard tracks" for example. What exactly does that mean?
I wonder how someone with more than 700 posts over here doesn't realize that Hydrogenaudio is a bit different (luckily)
Sorry Arnold if i made you upset in a way!

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AstralStorm
post Feb 16 2014, 21:22
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Yeah yeah. Blame the messenger. Please continue disregarding anything I'll say regardless of how ridiculously precise I have to be.
There *is* a difference. I don't know what causes it. It is inaudible on simple tracks (IMO), it is audible on hard tracks (single-blind test). Manifests to my ears as difference in timbre (read the definition of the word, I'm using the common one).
To be more exact, the difference sounded like extra "fatness" in the sound, as if everything was bassier or bass was "later". (Except there was no FR or phase response difference large enough to explain it.)

Arnold: Your graph is worthless, because you used (mostly) harmonically related frequencies. That doesn't work for IMD testing. Please check how CCIF IMD is done and how SMPTE IMD is done. The frequencies used in those do not have simple common divisors.
(E.g. CCIF: 19/20. SMPTE: 30/7.) Essentially your test is CCIF times 10. It is pretty hard, but only when tried in top octave. At low frequencies such simple ratios are generally handled well and SMPTE is harder. Then, there are even harder IMD tests with "weirder" ratios.
The problem with such test is that the spurious frequencies will reinforce and cancel each other very predictably since every pair of the frequencies is related with a relatively similar ratios or a close multiple of it.
Plus they're not 115dB down, subtract 30 dB... and you've made it easier on the opamp by reducing volume by that many dB. (I assumed those are dBV, not dBFS. If they're dBFS, please provide voltages.)

Sorry I haven't posted mine yet, various reasons which are not interesting to you I bet. I'll get on it next month. (and unfortunately no earlier)
The said chord is a really "wolf" chord, highly atonal, 5 tones. I'll try to find the file in the library, hopefully I won't have to recreate it.

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saratoga
post Feb 16 2014, 21:35
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QUOTE (AstralStorm @ Feb 16 2014, 15:22) *
Yeah yeah. Blame the messenger. Please continue disregarding anything I'll say regardless of how ridiculously precise I have to be.


This is kind of a silly thing to say given that you still haven't posted anything of substance.

QUOTE (AstralStorm @ Feb 16 2014, 15:22) *
Arnold: Your graph is worthless, because you used harmonically related frequencies.


800 and 900 Hz are harmonically related? No, no they're not.

His test contains both harmonic and non-harmonic frequencies, and so it can test for both THD and IMD.

QUOTE (AstralStorm @ Feb 16 2014, 15:22) *
That doesn't work for IMD testing.


You're mistaken. 800+900 = 1700Hz

From his graph you can see that IMD is less than -129 dB. Clearly this is negligible.

----

FWIW, THD is just a degenerate case of IMD. If THD is 6 orders of magnitude below relevance, probably IMD is negligible too!

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AstralStorm
post Feb 16 2014, 21:56
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It might be, but again, 8/9 is a relatively simple ratio and IMD is reduced at low frequencies. Try that with 863 and 917 Hz for example... Preferably mutually prime numbers. You should get a decent hash, but still not high (I'd expect -80 dB or better from a good implementation at low frequencies like these. At 2V RMS. This is usually decently well masked in real music. In higher frequencies, the masking is not as important and the amplifiers do worse.)
There are a few low prime ratios in there. (Note that full scale is -30 dB (which unit?). This is less than -95 dB best case to be nitpicky. Actually since when one can record -129 dB anyway (that's below thermal noise floor unless > 3x averaged), this graph is all kinds of fishy to me.
19/20 kHz CCIF IMD is invisible there and that does not mesh with measurements elsewhere.

Also the M-Audio 1010LT is actually excellent at IMD (at least SMPTE, I couldn't find CCIF but should be also very good) and not representative of most devices. It is better than Benchmark DAC1 and 2 for instance. Note that nowhere I said you need exotic components. NE5532's main weakness is low PSRR (esp. vulnerable to ground modulation) and I bet the M-Audio engineers thought very hard on solving that issue. (It is one of the top audio opamps, though due to this problem not the easiest to use.) CMRR and other variables are on par with top current opamps as long as NE5532 is reproduced in modern processes and with decent QC.

That said, it might not be IMD being responsible for what I hear, but something entirely different. IMD seems the only likely candidate of what we know about. In fact, it'd be great if a mod would split the thread.

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RSS Lo-Fi Version Time is now: 22nd October 2014 - 01:37