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Author Topic: 44k vs. 96k - a new discovery  (Read 15713 times)

Ivo

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44k vs. 96k - a new discovery
« on: October 13, 2004, 06:33:01 PM »

Dan,

may I ask about something which is rather musical than technical (although you suggest us to remain rather technical here), but still, even the convertors are mainly for making music ...Smile I know there are already miles of theoretical discussions on this topic, but my question and sharing come from a different, rather practical angle.
At times I had Mytek, I made thorough comparisons between identical recordings made in 44 and 96 and found I like 96 k somehow always more (more vivid detail as if - even after converting them back to 44 k).
I stayed in that conclusion firmly even after getting your great convertors and kept recording only in 96 k. Today (after getting an "esoteric" hint from Ted Nightshade) I tried again to compare and again found that there definitely IS a sound difference between 96 and 44 recordings of the same sources. But to my surprise I somehow was NOT that sure what I actually prefer now. I felt as if 96 k sounds a bit "sharper" , more "crisp" and also a tiny bit more "hollow" as if, whereas 44k sounded more round, smooth, warm , kind of "analog", more "friendly" I would say (not having those bright fingertips though). Although I did not want to admit that openly to myself (after advocating 96k for so long time), I felt that now I definitely prefer 44 k recording as more pleasant to my ears. What is your feeling and experience using these two frequencies for musical recording ? May it happen that the results may be convertor dependent..i.e. some convertor may sound better in 44, other in 96 or these frequencies have some general qualities which must be considered when making a choice ?
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Ivo

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zztim

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Re: 44k vs. 96k - a new discovery
« Reply #1 on: October 14, 2004, 12:43:35 PM »

hello, I've got the same surprise last year. I used MOTU I/Os to record guitars and drums using different sample rates. My subjective feeling of this records were better in the case of 44k. Instead of 96k. But, there were some difficulties in mixing & mastering in 44k. The presence of sound was not enough good. I solved these problems using the analog mixing.

 
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Bob Olhsson

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Re: 44k vs. 96k - a new discovery
« Reply #2 on: October 14, 2004, 11:49:52 PM »

The more I work with digital audio, the more I realize that most generalizations make little sense.

Dan wrote something very significant in his argument against ultra high sample rates. As you increase sample rate, you increase the requirement for precision. This is a generalization that not only makes sense but explains why in some cases working at a lower sample rate might well create less distortion than using the same tools at a higher sample rate.

ted nightshade

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Re: 44k vs. 96k - a new discovery
« Reply #3 on: October 18, 2004, 11:15:50 AM »

For the record, since I don't see it mentioned in his post, Ivo is using the Lavry Blue these days and that's what he used in his latest 44.1 vs. 96 experiment.
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Barry Hufker

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Re: 44k vs. 96k - a new discovery
« Reply #4 on: October 23, 2004, 02:50:59 PM »

I wonder whether the difference is 96k versus 44.1 or whether it is the implementation of antialiasing filters.  According to a presentation by Rupert Neve, there is only one A/D chip (a brand new one and he didn't mention the maker or model) that actually trades a little bit of flat response (down1dB at 20k) for much better antialiasing.  He explained that chip makers have put the emphasis on marketing a ruler flat frequency response rather than aliasing.  So would the aliasing be of the same quality for 96 and 44.1?  I don't know.  Would it be quality antialiasing to begin with?  I don't know.

I do know that very few hardware and software manufacturers actually make good sample rate converters.  You can find interesting information here: www.audioease.com/Pages/BarbaBatch4/Barba4SRCTest.html
And while Audio Ease does want to sell products and so who is to say if you can really trust their "research," I have done Audio Ease's test myself using Barbabatch and Peak.  The results were as posted.  So, I think there is a lot more to consider than just sampling rates.
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ammitsboel

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Re: 44k vs. 96k - a new discovery
« Reply #5 on: October 23, 2004, 04:02:47 PM »

Barry Hufker wrote on Sat, 23 October 2004 19:50

I wonder whether the difference is 96k versus 44.1 or whether it is the implementation of antialiasing filters.  According to a presentation by Rupert Neve, there is only one A/D chip (a brand new one and he didn't mention the maker or model) that actually trades a little bit of flat response (down1dB at 20k) for much better antialiasing.  He explained that chip makers have put the emphasis on marketing a ruler flat frequency response rather than aliasing.  So would the aliasing be of the same quality for 96 and 44.1?  I don't know.  Would it be quality antialiasing to begin with?  I don't know.


Depending on the filter type and components, some can really screw up the meaning by the music signal you put into them, and sometimes more than aliasing would do.
I think that 44.1 vs. 96 has a lot to do with the filters.
Maybe also the presison of the recieve/send circuits in our converters? has anybody done a test with Jitter and different sample rates?


Best Regards,
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danlavry

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Re: 44k vs. 96k - a new discovery
« Reply #6 on: October 23, 2004, 09:15:19 PM »

Barry Hufker wrote on Sat, 23 October 2004 19:50

I wonder whether the difference is 96k versus 44.1 or whether it is the implementation of antialiasing filters.  According to a presentation by Rupert Neve, there is only one A/D chip (a brand new one and he didn't mention the maker or model) that actually trades a little bit of flat response (down1dB at 20k) for much better antialiasing.....




I wonder how old is the Neve presentation. I would guess it is ten years old (or more). That anti aliasing filter problem was very serious some years ago, when the requirement to protect from aliasing was real tough. In the days before AD's were designed with oversampling front ends, one had to attempt and pass as near to 20KHz as possible (flat response) and than attenuate with a very high slope filter - very many poles, up to 22.050KHz.
That was a 2 KHz transition and took tons of opamps and precision parts, and the compromises were painful. And to add "insult to injury", phase non linearity at above 10KHz was always there...

But with oversampling front ends, AD anti aliasing became easier. In fact just a X2 oversampling makes the transition band about 20KHz (a factor of 10). Todays AD's IC's are almost all of the sigma delta types and they operate at 64Xfs to 512Xfs, and the anti alias filter problem is long gone... You can have a 3 pole filter at 40Khz yield 120dB protection with next to zero phase linearity impact. So it is not what it used to be.

You can still have problems in the digital decimation filter yielding that -1dB at 20KHz (for 44.1KHz), but it is not an anti ailaising filter issue.

BR
Dan Lavry
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Barry Hufker

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Re: 44k vs. 96k - a new discovery
« Reply #7 on: October 23, 2004, 11:45:34 PM »

Dan,

I head the 4-year undergraduate program in Audio Production at Webster University.  We invited Rupert Neve as a guest speaker.  I say this only to give you the circumstances under which Mr. Neve came to our campus this past spring to speak.  It was at that time (April or May of this year, I forget exactly), that Mr. Neve made the statement I attributed to him.  He even said this new chip was just coming out.

I was a witness to this statement, but this is not my area of expertise so I can't clarify it further.  But Mr. Neve spoke of it as an immediate (at that moment) development.

Barry
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Joe Bryan

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Re: 44k vs. 96k - a new discovery
« Reply #8 on: October 24, 2004, 02:45:09 AM »

It's very possible that the DC blocking filter in the converters is tracking the sample rate. I.e. as you go up in sample rate, the DC blocking filter's cutoff rises (1 Hz at 48k, 2 Hz at 96k, and 4 Hz at 192k).

The increasing phase shift from the DC blocking filter smears the low-end, and causes low-end transients (like kick) to loose their punch and transparancy. To me, it sounds like a window sliding up the spectrum, you loose low-end as you gain high-end.

This isn't a slam on high sampling rates, because there are some good converters that do this correctly, and these *do* sound better at higher rates despite technical arguments to the contrary (ears are the reference, not theory).

Also, in DSP systems, higher sampling rates do have advantages as well as disadvantages (higher processing load, more disk space/fewer tracks, etc.). Specifically, well designed DSP filters will sound better at higher sampling rates because their responses can more closely approach the ideal analog response (in technical terms, the s-plane to Z-plane warping is more linear). Conversely, poorly designed filters may sound worse, especially at low frequencies because of data precision issues.

Futhermore, at higher sampling rates, analog anti-aliasing and anti-imaging filter requirements are less stringent (allowing less phase shift in the main audio band), and system latency can be reduced so digital processors can be used in real-time monitoring situations (especially vocal tracking).

-Joe

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Nika Aldrich

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Re: 44k vs. 96k - a new discovery
« Reply #9 on: October 24, 2004, 02:58:11 PM »

Joe Bryan wrote on Sun, 24 October 2004 07:45

Specifically, well designed DSP filters will sound better at higher sampling rates because their responses can more closely approach the ideal analog response (in technical terms, the s-plane to Z-plane warping is more linear).


Not all filters perform better at higher sampling rates.  Some filters have greater accumulative error by using excess taps to perform the process.

Quote:

Futhermore, at higher sampling rates, analog anti-aliasing and anti-imaging filter requirements are less stringent (allowing less phase shift in the main audio band),


Not true.  Almost all anti-aliasing and anti-imaging filters that you are speaking of are digital and linear phase, so no phase shift issues are improved by higher sampling rates.  The analog filters in any oversampling filter these days have phase shift so far below our audible phase discernability that this is clearly not a factor.  Further, most high sample rate converters use the same analog anti-aliasing/anti-imaging filters as their lower sample rate brethren.

Indeed, the anti-aliasing and anti-imaging filters are less stringent at the higher sampling rates, but this only pertains to what you call "poorly designed filters."  Not all filters have to suffer from the problems of the poorly designed ones, and the better designed ones will perform the same at the lower rate as at the higher rate.  

Quote:

and system latency can be reduced so digital processors can be used in real-time monitoring situations (especially vocal tracking).


For the most part system latency is improved with higher sample rates, though there are some situations where latency takes a hit as sample rates increase.

Nika.
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Nika Aldrich

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Re: 44k vs. 96k - a new discovery
« Reply #10 on: October 24, 2004, 03:08:38 PM »

Barry Hufker wrote on Sat, 23 October 2004 19:50

I wonder whether the difference is 96k versus 44.1 or whether it is the implementation of antialiasing filters.  According to a presentation by Rupert Neve, there is only one A/D chip (a brand new one and he didn't mention the maker or model) that actually trades a little bit of flat response (down1dB at 20k) for much better antialiasing.  He explained that chip makers have put the emphasis on marketing a ruler flat frequency response rather than aliasing.  So would the aliasing be of the same quality for 96 and 44.1?  I don't know.  Would it be quality antialiasing to begin with?  I don't know.


Barry,

Good questions.  There is indeed a tendency for chip manufacturers to "borrow" a little bit of bandwidth above the Nyquist Frequency for their filter roll-off, knowing that the aliasing will still only enter the data stream above the audible range.  Take, for example, a 48kS/s sampling system and an ear that can only hear up to 20kHz.  We can do our filtering from 20kHz to 24kHz, but this requires a very steep filter which means a lot of filter coefficients and thus more on-chip RAM and greater processing abilities.  The alternative is that we could have our filter roll-off between 20kHz and 28kHz, knowing that the 4kHz of added aliasing is going to end up between 20kHz and 24kHz, above the audible range anyway.  

This approach is fairly common.

What you are pointing at is a very noticeable reality that simply because current converters DON'T sound the same between their 44.1kHz and 96kHz sample rates does not inherently mean that they CAN'T sound the same.  In the end, a converter designer does not actually have to sacrifice EITHER the flat response OR the aliasing.  They just have to spend a few extra cents on enough DSP power to do the job right.  If they do then we can all spend a lot less money on post-processing DSP because we can keep the material at the lower rate and get the same quality.

I thinik the chip you may be speaking about is the AKM AK5394A.  It is indeed a very good chip.

Nika.
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Barry Hufker

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Re: 44k vs. 96k - a new discovery
« Reply #11 on: October 24, 2004, 05:39:30 PM »

Nika,

I think you explained Mr. Neve's point exactly in a way I never could.  Thank you!

I will look into the chip you suggest in the hopes of understanding the technical aspects of all this a little better.

Barry
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bobkatz

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Re: 44k vs. 96k - a new discovery
« Reply #12 on: October 24, 2004, 07:10:51 PM »

[quote title=Nika Aldrich wrote on Sun, 24 October 2004 15:08]
Barry Hufker wrote on Sat, 23 October 2004 19:50

\\

Good questions.  There is indeed a tendency for chip manufacturers to "borrow" a little bit of bandwidth above the Nyquist Frequency for their filter roll-off, knowing that the aliasing will still only enter the data stream above the audible range.





Would you explain your reasoning, Nika, since the alias product is a difference product, which means, for example, a 1 kHz alias if the signal is 1 kHz above the Nyquist limit.

BK
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Nika Aldrich

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Re: 44k vs. 96k - a new discovery
« Reply #13 on: October 24, 2004, 08:11:41 PM »

bobkatz wrote on Mon, 25 October 2004 00:10

Would you explain your reasoning, Nika, since the alias product is a difference product, which means, for example, a 1 kHz alias if the signal is 1 kHz above the Nyquist limit.

BK


Bob,

The alias product is a difference product from the SAMPLING frequency, not the NYQUIST frequency.  Aliasing occurs at the absolute value of the difference of the multiple of the sampling frequency.  Therefore, in a 48kS/s sampling system, a 25kHz signal will alias at 23kHz.  A 47kHz or 49kHz signal will alias at 1kHz.  A 193kHz signal will also alias at 1kHz.  This is very rudimentary sampling theory.

We think of aliasing, therefore, as "mirroring" around the Nyquist frequency, or "folding back" for any frequencies up to the sampling frequency.  Any book on the subject of sampling will confirm this.

Nika.
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bobkatz

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Re: 44k vs. 96k - a new discovery
« Reply #14 on: October 24, 2004, 10:48:35 PM »

Thanks for the clarification!

BK
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