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Old 11th April 2012, 08:09 PM   #281
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Quote:
Originally Posted by Ken Newton View Post
That seemingly contradictory fact helped lead me to the hypothesis I had suggested in the final several paragraphs of post #120 here: Metrum Octave Dac - What are the Chips used

I suspect that much of the annoying subjective aspect of CD audio stems from the dynamic interaction of the MULTIPLE (at least two) sinc filter responses across the recording/playback chain. Remove either the ADC sinc response via apodising, or remove the DAC sinc repsonse via NOS and, viola', much more natural sounding reproduction results. I would add that while eliminating one of those two (at the least) sinc responses in the chain substantially improves the sound, it may also be that removing BOTH would improve the sound to it's ultimate point. Something which could be done using high sample rate audio.
If you chain linear phase brick-wall filters the result is the same sinc impulse response. You can't get any sharper than a brick-wall.

You can see and compare the effects of various filters by doing filtering "offline" in software on a PC. Try a blind test converting 192 or 96 KHz source to 44.1 or 48.

You could also test your hypothesis with a WM874x DAC that has the selectable filters and select the minimum phase apodizing filter response.

In my opinion, the fact that all the integrated filters are half-band and thus only 6 dB down at the Nyquist is worse than the ringing. Bruno Putzeys has also commented on the pre-echo caused by the in-band ripple.
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Old 11th April 2012, 08:57 PM   #282
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Quote:
Originally Posted by Ken Newton View Post
That seemingly contradictory fact helped lead me to the hypothesis I had suggested in the final several paragraphs of post #120 here: Metrum Octave Dac - What are the Chips used

I suspect that much of the subjectively annoying aspects of CD audio stems from the dynamic interaction of the MULTIPLE (at least two) sinc filter responses across the recording/playback chain. Remove either the ADC sinc response via apodising, or remove the DAC sinc repsonse via NOS and, viola', much more natural sounding reproduction results. I would add that while eliminating one of those two (at the least) sinc responses in the chain substantially improves the sound, it may also be that removing BOTH would improve the sound to it's ultimate point. Something which could be done using high sample rate audio.

Interesting, time to take out the DSO again see if I can measure any difference.

I have a 99 track Denon Test CD from 1993 (EC 3991-2), track 59 features an impulse recorded at 0 dB.
I ripped it to HDD and looked at the waveform in an ancient version of Cool Edit. At first it looked like there's indeed a lot of ringing in the waveform, but then I realized that the red dots are the samples and the blue line is what the waveform would look like after DA-conversion. Cool Edit shows the reconstructed analogue waveform with the dots where the actual sample was. Double-clicking on a dot shows the sample value of that dot in the decimal system.

So, if you ignore the blue line and connect the dots with straight lines, there's still ringing, but the amplitude is nowhere near as high as it would have been after DA-conversion. In other words: AD-conversion does create ringing, but not as much as DA-conversion. This should show on a measurement with my DSO.

It does, look at the results. It think this might answer the question why NOS may sound better despite (some) ringing in the AD-conversion stage.

From left to right:
- Waveform displayed by Cool Edit as if it were already DA-converted the traditional way;
- Octave, 44.1 kHz, only the ringing from AD-conversion;
- DAC1, 44.1 kHz, added ringing from DA-conversion OS-style;
- PDR-555RW, 44.1 kHz, added ringing from DA-conversion OS-style;

A bit off-topic, but I found out this way that the Micromega DAC1 has phase inverted on the unbalanced analogue output. To correct, I used the digital phase inversion-fucntion on the DAC1.
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File Type: gif dac1_imp_44k.gif (4.7 KB, 210 views)
File Type: gif 555_imp_44k.gif (4.8 KB, 186 views)

Last edited by jitter; 11th April 2012 at 09:10 PM.
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Old 12th April 2012, 12:48 AM   #283
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Quote:
Originally Posted by Ken Newton View Post
That seemingly contradictory fact helped lead me to the hypothesis I had suggested in the final several paragraphs of post #120 here: Metrum Octave Dac - What are the Chips used
Thanks for drawing my attention back to your earlier post. I hadn't fully digested the import of what you were suggesting there Yet even though I've mulled over your ideas some more now, I still have some nagging doubts...

Quote:
I suspect that much of the subjectively annoying aspects of CD audio stems from the dynamic interaction of the MULTIPLE (at least two) sinc filter responses across the recording/playback chain. Remove either the ADC sinc response via apodising, or remove the DAC sinc repsonse via NOS and, viola', much more natural sounding reproduction results.
Here's one of my concerns. You don't suggest a mechanism for how or where the imtermodulation between sinc artifacts occurs. In the case of a normal OS DAC with normal OS ADC this is presumably in the DAC chip and/or subsequent analog stage? Do you have any meat to put on the bones of this - for example could it be avoided without going to NOS?

Secondly, presumably in the case where some kind of ASRC has been used on a recording along with a normal ADC then there will already be two sinc responses embedded into the data. If your hypothesis is correct then ISTM those recordings won't sound truly NOS-like even when played back with a NOS DAC. Has anyone here found such a recording - one which nullifies the NOS sound?

Quote:
I would add that while eliminating one of those two (at the least) sinc responses in the chain substantially improves the sound, it may also be that removing BOTH would improve the sound to it's ultimate point. Something which could be done using high sample rate audio.
I can think of another interesting experiment - find out if any recordings use NOS ADC. I'm also curious to discover whether a non-OS apodizing filter does even better than NOS with no filter. I might even try this last experiment myself When I listened to my own designed min-phase apodizing filter at 2X OS I found the sound not to be as sweet as pure NOS - I put this down to increased glitchiness from the DAC when running at 88k2 rather than 44k1.
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Old 12th April 2012, 04:48 AM   #284
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Quote:
Originally Posted by abraxalito View Post
Thanks for drawing my attention back to your earlier post. I hadn't fully digested the import of what you were suggesting there Yet even though I've mulled over your ideas some more now, I still have some nagging doubts...
Thanks, for recognizing it.

Quote:
Here's one of my concerns. You don't suggest a mechanism for how or where the imtermodulation between sinc artifacts occurs. In the case of a normal OS DAC with normal OS ADC this is presumably in the DAC chip and/or subsequent analog stage? Do you have any meat to put on the bones of this - for example could it be avoided without going to NOS?
I agree with this statement. I have not suggested a fleshed out theoretical mechanism, and essentially admit as much in my comment #120. I wish that I had the mathematical analysis skills to perform a proper investigation in to what audibly occurs when either apodising or NOS are alternately implemented. My hypothesis about there being some kind of dynamic interaction, or, perhaps, some peculiar intermodulation between the recording and playback sinc filter responses is mostly based on logical deduction stemming from my empirical listening experiments with OS, NOS, and apodising filters.

Quote:
Secondly, presumably in the case where some kind of ASRC has been used on a recording along with a normal ADC then there will already be two sinc responses embedded into the data. If your hypothesis is correct then ISTM those recordings won't sound truly NOS-like even when played back with a NOS DAC. Has anyone here found such a recording - one which nullifies the NOS sound?
Yes, I should think that the only instances where more than two independent sinc filter responses would be involved is for sample rate conversion. I'm just now thinking that, perhaps, the independent aspect of the separated ADC and DAC sinc filters may be critical here. While most chip based OS filters are comprised of a chain of multiple smaller FIR units, such filter chains are coherently designed and implemented as a unified architecture. This is only conjecture, however, on my part.

This is an intriguing question. It may just be, that recordings which have been subjected to an ADC filter + ASRC filter + DAC filter won't sound particularly natural, even upon apodising or NOS.

Quote:
I can think of another interesting experiment - find out if any recordings use NOS ADC. I'm also curious to discover whether a non-OS apodizing filter does even better than NOS with no filter. I might even try this last experiment myself When I listened to my own designed min-phase apodizing filter at 2X OS I found the sound not to be as sweet as pure NOS - I put this down to increased glitchiness from the DAC when running at 88k2 rather than 44k1.
I believe that we share opinions regarding apodising vs. NOS. While I hear the same type of natural, or relaxed quality via apodising as I do via NOS, overall, apodising lacks treble energy, more so even than NOS. I suspect that you may find the same results for 44.1ksps apodising as for x2 OS apodising, depending on the stop-band frequency you are using. To effectively remove the ADC sinc filter ringing with a DAC apodising filter requires, from my observations, that FULL stop-band rejection occur by 19kHz-20kHz, not the 22.05kHz Nyquist frequency typically touted by vendors promoting their commercial apodising filters.

Having the stop-band at no higher than 20kHz means that the transition band will typically extend down to around 18kHz. This produced a much more obvious high frequency curtailment than did the -3dB@20kHz of NOS. While naturalness, clarity, and effortlessness was about equivalent between them, apodising's more obvious high roll-off tended to rob life from instrument harmonics, rendering the overall subjective presentation slightly inferior when compared to NOS.
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Last edited by Ken Newton; 12th April 2012 at 05:14 AM.
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Old 12th April 2012, 05:38 AM   #285
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Originally Posted by abraxalito View Post
I can think of another interesting experiment - find out if any recordings use NOS ADC.
I may be mistaken, but aren't SACDs (DSD) recorded sans any ADC anti-alias filtering, and played back sans any DAC digital reconstruction filtering? If so, it may explain the positive subjective qualities of SACD. One would think that some audiophile oriented label would have released some 96k sample rate high-res. tracks recorded without any ADC anti-alias filtering. Anti-alias filtering wouldn't seem to be necessary with a 48kHz frequency-domain signal bandwidth.

It's too bad that Sony chose such an unecessarily low quantizer resolution, given that the x64 oversampling ratio also chosen really isn't very high, even using high-order noise-shaping. But that is another can of worms.
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Old 12th April 2012, 05:48 AM   #286
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Yep I believe that's so - however SACD is S-D and therefore by definition must suffer from noise modulation effects... I was thinking of getting hold of one of ADI's newest breed of ADCs based on SAR (rather than S-D) for my projects. They look really good spec-wise and have become quite affordable - http://www.analog.com/static/importe...8-1_7988-5.pdf
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Old 12th April 2012, 05:56 AM   #287
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Hi,

Quote:
Originally Posted by abraxalito
I can think of another interesting experiment - find out if any recordings use NOS ADC.
Many early CD's where made with Sony Processors that operated at 1 X FS sample rate. Apogee got their start in digital audio by making replacements for the elliptical LC filters for these machines. Other processors often worked the same. It too a fair bit of time for oversampling to gain wide use in the industry. Audiophile Labels where the early adopters. Sadly there is no way to tell for sure.

Quote:
Originally Posted by Ken Newton View Post
I may be mistaken, but aren't SACDs recorded sans any ADC anti-alias filtering or DAC digital reconstruction filtering? If so, it may explain the positive subjective qualities of SACD. It's too bad that Sony chose such an unecessarily low quantizer resolution, given that the oversampling ratio also chosen isn't that high at x64.
SACD is basically the DS Modulator output from a generic ADC originally meant for transferring analogue recordings for later release on CD. On a fundamental level the principle is flawed, both due to the DS nature and the fact that for the claimed dynamic range and bandwidth the required dither would overload the modulator.

This is generally shown by the simple observation that most (all? - but I have not measured all) SACD Players have a rising noisefloor in the audio range and by 20KHz have only comparable SNR to CD. While I am not in general a fan of adding dither, in principle CD can achieve a similar result using suitably noiseshaped dither during the mastering.

I suspect "pure" SACD primarily sound better than their PCM counterparts because editing and applying effects to DSD is even now not well and widely supported, compared to the proliferation of such tools in the "PCM Universe", where so many dynamic range and other effects are now routinely applied that to my "old skool analogue minimalist recording" ears even recordings that are by todays standards nearly untouched sound sound over-produced and overcooked.

With SACD it is actually very hard to get the same kind of sound (unless mastering and applying FX in PCM and then converting to DSD) so the sound of DSD based recordings often more closely resembles reality.

THAT SAID, really good CD-Recordings using really high grade CD-Replay, to my ears at least (and as I demonstrated in the early 2K's at a few London HiFi Shows to many others) can achieve the same or greater subjective sound quality as that offered by SACD.

Ciao T
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Old 12th April 2012, 06:08 AM   #288
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Quote:
Originally Posted by ThorstenL View Post
Many early CD's where made with Sony Processors that operated at 1 X FS sample rate. Apogee got their start in digital audio by making replacements for the elliptical LC filters for these machines.
However in those days, dither was not really well understood amongst the broad sweep of designers (I'll pre-empt Thorsten saying 'nothing's changed there then'). I recall someone (I think it was Paul Frindle) telling me that the replacements were initially lower noise but sounded worse. Until someone woke up to the fact that the circuit noise was providing the necessary dither to linearize low-level performance. Increasing the noise from the earliest Apogee filters improved the sound. (I could have got this story a little bit garbled over the intervening time - so if somebody's got a less fogged version please chime in ).

Also generally ADC linearity sucked then too. Crystal only came out with its fiendishly clever self-calibrating CMOS switched-capacitor ADC designs in the mid 80s I seem to recall and even then they started out at 12bits.
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Old 12th April 2012, 06:09 AM   #289
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Hi,

Quote:
Originally Posted by abraxalito View Post
I was thinking of getting hold of one of ADI's newest breed of ADCs based on SAR (rather than S-D) for my projects. They look really good spec-wise and have become quite affordable - http://www.analog.com/static/importe...8-1_7988-5.pdf
These look nice.

Personally I'd probably want to stack 8 pcs per channel run interleaved with a suitable following summing logic based NOT on classic digital filters. This should allow effective 16 X Oversampling at 192KHz, or the addition of 8 more encodable levels, giving us 18-19 usable bits, which should suffice where 16 Bit may not.

Ciao T
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Old 12th April 2012, 06:14 AM   #290
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I listened to my own designed min-phase apodizing filter at 2X OS I found the sound not to be as sweet as pure NOS - I put this down to increased glitchiness from the DAC when running at 88k2 rather than 44k1.
One final thought about the subject of apodising not sounding as sweet. Try reversing the absolute phase when listening to the apodising filter versus NOS. It may make no difference, but I regularly find that the absolute phase needs to be reversed (much to my annoyance) when switching from one digital reconstruction filter algorithm to another, else the sound be grainy or less sweet.
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Last edited by Ken Newton; 12th April 2012 at 06:18 AM.
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