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Help! Sacd Good Or Bad?, Does SACD ought to sound like crud?
Joe Bloggs
post Sep 9 2002, 12:33
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I've listened to SACD once and it sure sounded good...

I've heard people say that SACD ought to fail in transient reproduction, (because it can only encode a rise and fall relative to the last time step) so I did some calculations:

'Sampling rate' of SACD = 2.8MHz = 64x 44.1kHz

For encoding tones up to 44.1kHz at full scale, it has to reach full-scale from 0 in 64 steps, that is, at any given time there can only be 64 possible positions for the waveform.

This gives it 6 bits resolution to CD's 16 bits??

OK, suppose you only need to encode up to 22.05kHz at full scale, the number of possible positions increases from 64 to 128--7 bits resolution, big improvement blink.gif

I doubt this is how DSD actually works, but this article http://www.iar-80.com/page40.html (I linked to page 40, but it seems page 1-39 may be going on and on about the sonic flaws of DSD as well) seems to take this view seriously and goes on to talk about how you try to recover musical information from the 6 bit stream. blink.gif
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Frank Klemm
post Sep 10 2002, 01:25
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QUOTE (2Bdecided @ Sep 9 2002 - 06:49 PM)
IIRC, the difference between delta and sigma-delta is basically this:

delta: you integrate (sum) the output
sigma-delta: you integrate (sum) the input


The (not too obvious) result is that, while delta modulation can suffer from slope overload (which is what you're describing - the 22kHz sine wave is moving far too quickly for the digital staircase to track it), sigma-delta modulation does not. However, the higher frequencies are full of noise.

Think of it this way: in a basic delta modulator, if you draw a graph of frequency against allowed amplitude, then you are allowed high amplitudes at low frequencies, but only lower amplitudes and higher frequencies (otherwise you push it into slope overload).

However, in a sigma-delta system, it's as if the signal is "equialised" on the input to reduce the higher frequencies (to prevent slope overload), and then re-equalised on the output, to bring the higher frequencies back to their correct level. The result is that the higher frequency ranges contain much more noise - the modulator has an intrinsic noise, and it's amplified at higher frequencies on the output.


This is a very badly remembered way of thinking about it, and it's not quite how it works in reality. But I hope it helps!


So, basically, SACD has about 20 bits of equivalent resolution in the audio band, but terrible amounts of high frequency noise. It also has excellent time resolution. It sounds very good - whether all that high frequency noise is a good idea is a different matter entirely!

Cheers,
David.

Some of the technical flaws of SA-CD:

* If you want to do some digital post processing, you must convert
it to PCM. If PDM has any advantage, this advantage is removed.

Digital post processing can be
- digital filters for loudspeaker/room acoustic equalization
- digital filters for splitting the signal for 2/3-way loudspeakers
- digital filters for sound control (more complex equalizers)

* PDM is also not suitable to directly drive digital power amplifiers.
It switches too often so you have to much switching losses.
So PDM must converted to PCM and then to PWM.

* PDM is may be suitable to built low cost head phone DA/C+Amplifiers.

* PDM is very sensitive to asymmetries between switch on and switch off.

* Best possible converters (noise + linearity at low levels) do NOT use PDM, but
- PWM
- 4...16 PDM convertes in parallel
Both can not be generated by PDM, but by a PCM.

*The frequency response of the output filter of a SA-CD is not defined

- So it is not possible to compensate the effect of the output filter in the recording
- It is very likely that manufacturs built gadgets with extremely wide frquency response
and huge amounts of HF noise to boast with a extremely wide frequency response.

A proposal of such a filter should look like:

* 4th order LR-filter with f_{-6dB} = 48 kHz
12 kHz: -0.03 dB
24 kHz: -0.53 dB
48 kHz: -6.02 dB
96 kHz: -24.61 dB
192 kHz: -48.20 kHz
384 kHz: -72.25 kHz

Depending on the high frequency amount the frequency overall-frequency response
can be linearized up to 60 kHz (Pop) or 80 kHz (Classic).

-------------------------------------------------------------
Another point:
I have serious doubts about the need of a higher time resolution.
- Modern perceptial encoder has lime resoution between 1.5 and 5 ms.
- Very critical signal needs time resolution of 2...0.5 ms for f=10 kHz.
- CD has something in the range of 0.2...0.3 ms for f=20 kHz and 0.04 ms for f=10 kHz.
- DVD-A (96 kHz) has something in the range around 0.015...0.02 ms for f=20 kHz and
0.01...0.015 ms for f=10 kHz.


--------------------
-- Frank Klemm
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Posts in this topic
- Joe Bloggs   Help! Sacd Good Or Bad?   Sep 9 2002, 12:33
- - Joe Bloggs   Ok, um, does DSD assume delta modulation or delta-...   Sep 9 2002, 13:33
- - Peter   well, some people are apparently having problems w...   Sep 9 2002, 13:50
- - Joe Bloggs   Problem is, the bits are not employed in the same ...   Sep 9 2002, 14:15
- - Joe Bloggs   This is an example of Sigma-Delta, or Pulse Densit...   Sep 9 2002, 15:16
- - Jasper   The general idea is correct, but SACD quality does...   Sep 9 2002, 16:29
- - Joe Bloggs   So the encoding system is really just plain delta ...   Sep 9 2002, 16:39
- - Jasper   Sorry to have confused you, I didn't have a go...   Sep 9 2002, 16:54
- - 2Bdecided   IIRC, the difference between delta and sigma-delta...   Sep 9 2002, 17:49
- - n68   yup... call it what you wan`t... (i assume...   Sep 9 2002, 18:24
- - mcg1969   I don't think you can fairly say that SACD is ...   Sep 9 2002, 23:42
- - Frank Klemm   QUOTE (2Bdecided @ Sep 9 2002 - 06:49 PM)IIRC...   Sep 10 2002, 01:25
- - crazyboy_T   > - Very critical signal needs time resolution ...   Sep 10 2002, 04:22
- - n68   QUOTE (mcg1969 @ Sep 9 2002 - 10:42 PM)I don...   Sep 10 2002, 10:44
- - Pio2001   QUOTE (crazyboy_T @ Sep 10 2002 - 06:22 AM)Is...   Sep 10 2002, 11:47
- - Frank Klemm   QUOTE (crazyboy_T @ Sep 10 2002 - 05:22 AM)...   Sep 10 2002, 11:57
- - 2Bdecided   It's possible to detect an interaural time del...   Sep 10 2002, 12:36
- - petracci   QUOTE (2Bdecided @ Sep 9 2002 - 06:49 PM)Howe...   Sep 10 2002, 14:53
- - Joe Bloggs   QUOTE Another point: I have serious doubts about t...   Sep 10 2002, 15:01
- - Joe Bloggs   OT: I'd finally figured out what the correct g...   Sep 10 2002, 15:09
- - KikeG   QUOTE (Joe Bloggs @ Sep 10 2002 - 03:01 PM)I ...   Sep 10 2002, 21:27
- - bryant   QUOTE (Joe Bloggs @ Sep 10 2002 - 06:09 AM)OT...   Sep 10 2002, 22:33
- - Kim_C   QUOTE (KikeG @ Sep 10 2002 - 11:27 PM)QUOTE (...   Sep 11 2002, 02:51
- - Artemis3   So in other words, the answer to the thread's ...   Sep 11 2002, 04:19
- - Joe Bloggs   Huh? Plain DVD does 24/96? What's DVD-A for th...   Sep 11 2002, 05:42
- - bryant   QUOTE (Joe Bloggs @ Sep 10 2002 - 08:42 PM)Hu...   Sep 11 2002, 05:52
- - Joe Bloggs   Any DVD-A records with DRM?   Sep 11 2002, 06:45
- - bryant   QUOTE (Joe Bloggs @ Sep 10 2002 - 09:45 PM)An...   Sep 11 2002, 07:12
- - Joe Bloggs   Oh, I mean, any DVD-As without audible watermarks?   Sep 11 2002, 07:37
- - n68   QUOTE (bryant @ Sep 11 2002 - 06:12 AM)All DV...   Sep 11 2002, 08:08
- - bryant   QUOTE (Joe Bloggs @ Sep 10 2002 - 10:37 PM)Oh...   Sep 11 2002, 09:24
- - Pio2001   QUOTE (Kim_C @ Sep 11 2002 - 04:51 AM)Audio N...   Sep 11 2002, 11:46
- - Joe Bloggs   So would you agree with this kind of design? What...   Sep 11 2002, 13:33
- - ChristianHJW   Sorry for stepping is so late .... DVD-A vs. SACD ...   Sep 11 2002, 14:26
- - Frank Klemm   QUOTE (ChristianHJW @ Sep 11 2002 - 03:26 PM)...   Sep 11 2002, 14:54
- - user   DVD-Video: Theoretical PCM possibilities for DV...   Sep 11 2002, 14:55
- - ChristianHJW   QUOTE (Frank Klemm @ Sep 11 2002 - 01:54 PM)I...   Sep 11 2002, 15:11
- - Joe Bloggs   OK, so non-oversampling DACs use analog filtering ...   Sep 11 2002, 15:29
- - ChristianHJW   .. arent most modern DACs using a combination of d...   Sep 11 2002, 15:37
- - Kim_C   QUOTE (Pio2001 @ Sep 11 2002 - 01:46 PM)For w...   Sep 11 2002, 16:43
- - Joe Bloggs   What troubles me is that I don't even know wha...   Sep 11 2002, 16:51
- - Pio2001   QUOTE (Joe Bloggs @ Sep 11 2002 - 05:29 PM)Ca...   Sep 11 2002, 20:12
- - Frank Klemm   QUOTE (Joe Bloggs @ Sep 11 2002 - 06:42 AM)Hu...   Sep 11 2002, 20:49
- - KikeG   About non-oversampling filters, I have to say that...   Sep 12 2002, 00:45
- - Kim_C   QUOTE (KikeG @ Sep 12 2002 - 02:45 AM)About n...   Sep 12 2002, 13:53
- - 2Bdecided   I've heard David Chesky's 6 channel 24/96 ...   Sep 12 2002, 14:33
- - KikeG   In reply to Kim_C: It is true that human ear cann...   Sep 12 2002, 14:49
- - Kim_C   QUOTE (KikeG @ Sep 12 2002 - 04:49 PM)This do...   Sep 12 2002, 15:20
- - Kim_C   QUOTE (2Bdecided @ Sep 12 2002 - 04:33 PM)P.S...   Sep 12 2002, 15:52
- - Joe Bloggs   QUOTE (2Bdecided @ Sep 12 2002 - 09:33 PM)P.S...   Sep 12 2002, 16:20
- - KikeG   QUOTE (Kim_C @ Sep 12 2002 - 03:52 PM)"b...   Sep 12 2002, 16:51
- - ChristianHJW   QUOTE (KikeG @ Sep 12 2002 - 01:49 PM)In repl...   Sep 16 2002, 12:41
- - Joe Bloggs   I would also think that you're most likely to ...   Sep 16 2002, 13:03
- - KikeG   QUOTE (ChristianHJW @ Sep 16 2002 - 12:41 PM)...   Sep 16 2002, 18:56
- - Pio2001   QUOTE (ChristianHJW @ Sep 16 2002 - 02:41 PM)...   Sep 16 2002, 23:25
- - ChristianHJW   it was an analog filter i had done using a few op-...   Sep 17 2002, 10:39
- - fewtch   Sheesh... all of this started from an original que...   Sep 17 2002, 10:49
- - Pio2001   QUOTE (ChristianHJW @ Sep 17 2002 - 12:39 PM)...   Sep 17 2002, 11:32
- - fewtch   bleep   Sep 17 2002, 12:12
- - KikeG   QUOTE (ChristianHJW @ Sep 17 2002 - 10:39 AM)...   Sep 17 2002, 12:32
- - ChristianHJW   QUOTE (KikeG @ Sep 17 2002 - 11:32 AM)In the ...   Sep 17 2002, 13:31
- - Joe Bloggs   He said analog filter. The most likely explanation...   Sep 17 2002, 16:01
- - KikeG   QUOTE (ChristianHJW @ Sep 17 2002 - 01:31 PM)...   Sep 17 2002, 17:17
- - Pio2001   QUOTE (KikeG @ Sep 17 2002 - 02:32 PM)You can...   Sep 17 2002, 22:40
- - ChristianHJW   QUOTE (KikeG @ Sep 17 2002 - 04:17 PM)It is a...   Sep 19 2002, 13:56
- - KikeG   Well, I was just intending to explain that this ...   Sep 19 2002, 22:18
- - DickD   Regarding the airy sensation, I concur with KikeG....   Feb 11 2003, 14:41
- - robUx4   QUOTE (KikeG @ Sep 19 2002 - 10:18 PM)About f...   Mar 3 2003, 15:00
- - ChristianHJW   QUOTE (robUx4 @ Mar 3 2003 - 02:00 PM)We basi...   Mar 3 2003, 15:35
- - 2Bdecided   Most of the ideas that are being kicked around her...   Mar 3 2003, 16:02
- - user   http://www.hfm-detmold.de/texts/de/hfm/eti...ten/s...   Mar 3 2003, 16:04
- - ChristianHJW   QUOTE (user @ Mar 3 2003 - 03:04 PM)So, they ...   Mar 3 2003, 16:28
- - Frank Klemm   QUOTE (2Bdecided @ Mar 3 2003 - 05:02 PM)Most...   Mar 3 2003, 19:25
- - robUx4   That would be a very interresting stuff. How many ...   Mar 4 2003, 00:09
- - Pio2001   I've got a 24/96 soundcard, and HD 600 Headpho...   Mar 4 2003, 01:06
- - KikeG   I agree pretty much with Pio's explanations an...   Mar 4 2003, 09:46
- - KikeG   QUOTE (robUx4 @ Mar 3 2003 - 03:00 PM)... but...   Mar 4 2003, 09:50
- - Canar   This is completely off-topic, but I just wanted to...   Mar 4 2003, 10:15
- - robUx4   I just wanted to add something to my paleonthologi...   Mar 4 2003, 10:41
- - Pio2001   QUOTE (robUx4 @ Mar 3 2003 - 05:00 PM)The hum...   Mar 4 2003, 12:29
|- - user   interesting study and paper about difference betwe...   Mar 24 2006, 15:26
- - Pio2001   I remember having read this. It must have been dis...   Mar 24 2006, 16:27
- - SebastianG   I wonder why they have chosen 176,4 kHz at 24 bits...   Mar 24 2006, 16:58
- - Pio2001   Probably to stay close to real-world applications.   Mar 24 2006, 17:36


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