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Topic: Successful ABX of TPDF white dither vs. noise-shaping at normal listen (Read 35876 times) previous topic - next topic
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Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #25 –
When I subtract the two 16-bit samples (tpdf and shaped), the result is pure noise with no discernible details at any playback level. I think that implies that the only difference between the samples is dither.

I have also resampled the float version by 2463.596841 samples and it now subtracts very well with the 16-bit versions. There are some very low-level remnants of the music audible below the hiss, but I believe that those are a result of differences between the resampler Audacity uses and mine (and again it’s identical in both versions). I have uploaded this resampled file.

I don’t think there’s anything wrong with the dithering here.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #26 –
Quote from: bryant on
When I subtract the two 16-bit samples (tpdf and shaped), the result is pure noise with no discernible details at any playback level. I think that implies that the only difference between the samples is dither.

I have also resampled the float version by 2463.596841 samples and it now subtracts very well with the 16-bit versions. There are some very low-level remnants of the music audible below the hiss, but I believe that those are a result of differences between the resampler Audacity uses and mine (and again it’s identical in both versions). I have uploaded this resampled file.

I don’t think there’s anything wrong with the dithering here.

Thanks bryant.  On my equipment your resampled version does null very effectively against either of JSW's dithered versions, in terms of the audible result for my ears.  Ordinarily I would simply accept that result as indicating that for practical purposes the files are the same.

However I am already on record in this thread as claiming to have heard a difference!  [I did some informal ABX tests involving only 5 or 6 trials being concious of TOS#8; I'll do some longer tests over the weekend.]  In particular I found the TPDF version to sound duller than the floating point version.

So what is the explanation?  I am middle-aged.  I do not have exceptionally extended high frquency hearing.  The dither amplitude involved ought to be very small.  By itself dither can be audible at a high listening volume with a quiet passage.  As ChrisH has remarked, the particular recording already has sufficient noise so as not to need any dither! I don't have time this evening to do more tests.  I will try to post again on the weekend.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #27 –
Quote from: bryant on
I have also resampled the float version by 2463.596841 samples
I still don't get it. When investigating the effects of dither, there should be no need for resampling. There should be only one unique source and the sample rate should not be changed, otherwise too many variables are introduced and no meaningful conclusions can be drawn.
Now which file can be used as a source ?

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #28 –
You mean: where is the 24-bit 44.1kHz version that the two (first posted) different 16-bit versions were actually generated from?

Cheers,
David.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #29 –
I think I am coming around to JSW's point of view.  His TPDF file does seem to give a slightly clearer sound than his noise-shaped version. [It also happens to sound slightly less bright to my ears.]  However I am struggling to obtain persuasive ABX results.  After a few comparisons my brain starts to hear the alternatives as being the same!  It might help if someone else, with keen hearing, can attempt an ABX.  What this may end up telling us is that the noise-shaped dither implemented in JSW's version of Audacity is affecting the perceived quality of the audio.  I would reiterate that I am not talking about quiet passages played back at high gain.  I am actually talking about moderately loud passages played back at a normal gain setting.  (I have been listening with loudspeakers: headphones did not make the ABXing any easier.)

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #30 –
Quote from: 2Bdecided on
You mean: where is the 24-bit 44.1kHz version that the two (first posted) different 16-bit versions were actually generated from?

Cheers,
David.


The 24/44.1 common source for my 16-bit uploads doesn't exist.  It never did, except one sample at a time--in floating point--when my computer created my 16/44.1 files.  I you think about it, you will realize that the exact same resampling must have been performed twice, once for each file, and the results destroyed as soon as they were created.  When asked for a 24/44.1 file, I made a conscious decision whether to reconstruct this hypothetical source file or else provide an equivalent file representing the exact same content in another frame of reference.  I chose the latter, in part because it was easier to do and in part because I thought that doing it this way might elicit a more interesting reaction.  It did.

People are finding that the downsampled files require more care in handling than what they are used to, and that the presence of musical content very close to fs/2 is getting in the way of the signal processing that they want to do.  For me, there's an obvious solution: PCM audio content ought to have a silent band between fs/2 and, say, fs/2.2, so that interpolation filters can do their work without details of the transition band having any effect on the output.  On these grounds, by the way, I am opposed to UV-22 and any other method that creates a lot of noise close to fs/2.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #31 –
I for one would feel more comfortable with this if an original 24/44.1 sample were to be made available which, when processed in the aforementioned manner, produced a dithered 16/44.1 resultant file which could then be ABXed. In this way, anyone can take the original file and process it themselves to ensure repeatability of the process.

Given that dither is generally not heard and that for this sample it is, repeatability is vital.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #32 –
I agree with Nick.C. If this test is to mean anything, we need the source material.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #33 –
Quote from: C.R.Helmrich on
Plus, I'd like to note that for our current sample recording, we wouldn't even need dither, as the recording itself contains enough noise. Saves us a few dB in shaped-noise energy.


Interesting.  Can you confirm that the noise is electronic in origin?  Orchestra hall in Minneapolis is an unusual hall.  It was designed for an exceptionally flat reverb time across the gamut, and has hard polygonal surfaces on the ceiling and behind the stage that scatter sound rather than absorbing it.  This way, concerts sound brighter than at most other venues, and the sound is remarkably consistent from seat to seat.  In the recording, therefore, what looks like broad-spectrum background noise might actually be reverberation.  This noise would then not be present at the beginning of a piece.

In any case, I should think it is always safer to dither.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #34 –
Quote from: Nick.C on
I for one would feel more comfortable with this if an original 24/44.1 sample were to be made available which, when processed in the aforementioned manner, produced a dithered 16/44.1 resultant file which could then be ABXed. In this way, anyone can take the original file and process it themselves to ensure repeatability of the process.

Given that dither is generally not heard and that for this sample it is, repeatability is vital.


The original source file is publicly available, and I have specified the algorithm used to process it.  I think it is well established that my files are reliable, and am not going to waste part of my upload quota proving it.

If anybody succeeds in ABX'ing my flat-dithered file against one made from the floating-point file, then I'll reconsider my position.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #35 –
Bleh. Missed the Uploads link. Sorry JSW.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #36 –
Quote from: JSW on
The original source file is publicly available, and I have specified the algorithm used to process it.  I think it is well established that my files are reliable, and am not going to waste part of my upload quota proving it.
Which one in the upload thread is the original?

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #37 –
My assumption was the floating-point version.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #38 –
Quote from: JSW on
If anybody succeeds in ABX'ing my flat-dithered file against one made from the floating-point file, then I'll reconsider my position.
To use JSW's float file for ABXing against JSW's two dithered files, 2463 or 2464 samples (around 56mS) need to be excised from the start of it. Alternatively bryant's resampled version (a precision time alignment by 2463.596841 samples) could be used.

Quote from: JSW on
To me, it sounds like the problem you are having is confirmation of my thesis: flat dither to 16 bits is not transparent with this material, while standard noise shaping changes the tone color (probably by partially masking the high-frequency content).

JSW, there is a lot going on when converting from a SR of 96KHz to 44.1KHz.  You appear to be very knowledgeable.  You would be aware that an audio engineering decision needs to be made as to exactly how to filter the audio that lies near the target fs/2, taking into account the competing considerations of extended frequency response and minimising phase changes.  44.1KHz does not give a lot of headroom; 48KHz would be less challenging.  Also, when playing back a file, the DAC used may behave differently when processing different SRs.  As the differences between dithers can be expected to be very subtle, it is desirable to eliminate other subtle factors.

So if on given equipment 16/44 TPDF is not transparent relative to an original 24/96 file, that would call into question not just the dither, but the sample rate conversion to create the 16/44 file; as well as the performance of the sound card or other device being used to compare the 16/44 with the 24/96.

Because of the above, it would desirable if all parties were working from a unique 24/44 file.  They could then compare how different dithers (including no dither) sounded when the 24/44 file was bit depth reduced to 16/44.  I note that even if I downloaded the 24/96 track for the very modest fee involved, and located the correct sample position for time alignment, I would then be faced with the decision of what filter to use to create a 24/44 reference file.  For example, I imagine that different versions of Audacity do not necessarily use the same filters when converting between sample rates.  Cheers.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #39 –
I don't know how many forum members are aware of the July 2005 Stereophile article Contingent Dither by Keith Howard, that can be found at http://www.stereophile.com/features/705dither/index.html

On page 3, the article states:
[blockquote]
Quote
The Sound of Dither
We've seen that most of the 24-bit recordings I've analyzed can be truncated to 16-bit sans dither without this introducing many—sometimes any—signal-correlated quantization errors that are detectable either by listening to the quantization error or by applying the lag 1 autocorrelation test.
[/blockquote]
The article doesn't include ABX test results but discusses some issues relevant to this thread.  (I apologise if this article has previously been dissected/discussed somewhere on HA but the search string "contingent dither" does not result in a hit using Google Search restricted to HA.)

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #40 –
The content of PCM data is the bandwidth-limited function that passes through all the sample points.  In other words, it is the result of interpolating with an ideal sinc filter.  Of course, an ideal sinc filter cannot be implemented, which means that when the PCM file contains a lot of power very near fs/2, actually determining the content is very problematic.  I'm not sure whether this content can even in principle be calculated accurately for a single interpolation point.  You'll have to ask a professor of numerical mathematics.  There's a good chance he'll tell you that the computation is numerically unstable, and it's even possible he'll tell you that it involves calculating a sum that is not well defined.

On the other hand, when the PCM file has a silent band right below fs/2, the content is very easy to compute to any degree of accuracy: you simply use an interpolation filter that has its transition band contained within that silent band.

The floating-point file I uploaded has the same content as the hypothetical one that could have generated my 16-bit files, in the following sense: the 24/96 file downloaded from HDTracks was produced using a gentle low-pass filter, and is very silent above 40kHz.  Its content is therefore unambiguously defined.  You get the content of my floating-point file, and the content before dithering of my 16-bit files, by taking the content of the 24/96, low-pass filtered by the "high-quality sinc filter" implemented in Audacity 1.2.6a for Mac PPC.  Going back to the original 24/96 file therefore resolves all questions.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #41 –
Quote from: JSW on
The floating-point file I uploaded has the same content as the hypothetical one that could have generated my 16-bit files, in the following sense: the 24/96 file downloaded from HDTracks was produced using a gentle low-pass filter, and is very silent above 40kHz.
The emphasised portion of the above statement has me concerned.

For clarity, I would appreciate an original sample (up to 30 seconds) which can then be processed.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #42 –
I note that this thread is about bit depth and dither (rather than a sample rate of 96KHz vs 44.1KHz).

I seems the whole exercise of creating and uploading files needs to be redone to ensure perceived and actual repeatability.

If we can confirm that ETsample_float.wav contains music data beyond 16 bits of resolution then that file could be used as a suitable reference from which to create 16 bit files with, say, a recent version of Audacity, and in the following flavours of dither:  TPDF, noise shaped, and none.

[I have not been able to analyse ETsample_float.wav for its underlying equivalent integer based bit depth.  Has anyone else been able to do so?  Or is this something too diifficult to do in the presence of noise? ]

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #43 –
The problems people have had with my files would never have come up if these files were simply used for the intended purpose (applying different kinds of dither, followed by listening tests); moreover, resampling would not have posed difficulties of any kind if there had been a silent band at the top.  I think I have just presented a fairly cogent argument that the most useful form for content intended for CD release is in fact files at 20/48 or 24/48, encoded using an antialiasing filter with 22kHz stopband, and that these should therefore be the preferred formats in recording and high-quality file exchange.  They have the added benefit that you can encode them on DVD-V without modification.

P.S. The ABX software that I used automatically discards the appropriate of samples to make sure the test is aligned adequately.  I just assumed that everybody has that capability.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #44 –
The problem is that there is no original as yet readily available to us to duplicate your processing - only two modified samples. I don't understand your perceived reluctance to post an original sample.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #45 –
Quote from: Canar on
I agree with Nick.C. If this test is to mean anything, we need the source material.



Totally agreed.

I'm very confused about what the actual source material was with any degree of specificity.

The basic work seems to be downloadable from

http://www.hdtracks.com/index.php?file=cat...=HD030911109622

But that is almost 57 minutes of music. I get the impression that the alleged difference is strongest at a certain point in the work. If the reference work were given as one of the 9 seprately-downloadable tracks, that would be an improvement.

However, there should be no problem with a unploading a short excerpt that deserves exemption under the "fair" use provisions of the copyright law - as a scientific investigation. HA's TOS specifically allows this.

There seem to be a lot of questions about exactly what is being compared and what has been compared under reliable (TOS 8) circumstances. I fear that a lot of sighted evaluations are getting slipped into the HA record.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #46 –
Quote from: Arnold B. Krueger on
I'm very confused about what the actual source material was with any degree of specificity.
The OP gave a link to the uploaded sources in post 5 but it's rather easy to miss, so here they are again:

Quote from: JSW on
ETsample_shaped.wav
ETsample_TPDF.wav
Here are samples from 28.846154-43.461538 seconds into the tracks I discussed in my "listening tests" post.  Good luck!  The difference between these tracks is very subtle.

Quote from: JSW on
And here, by popular request, is approximately the same passage at 44.1 kHz, floating point resolution.
ETsample_float.wav

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #47 –
Quote from: Kees de Visser on
Quote from: Arnold B. Krueger on
I'm very confused about what the actual source material was with any degree of specificity.
The OP gave a link to the uploaded sources in post 5 but it's rather easy to miss, so here they are again:

Quote from: JSW on
ETsample_shaped.wav
ETsample_TPDF.wav
Here are samples from 28.846154-43.461538 seconds into the tracks I discussed in my "listening tests" post.  Good luck!  The difference between these tracks is very subtle.

Quote from: JSW on
And here, by popular request, is approximately the same passage at 44.1 kHz, floating point resolution.
ETsample_float.wav




There' seems to be a failure to communicate here. Part of a complete package, and file that is thusfar missing is the relevant excerpt of the file downloaded from www.hdtracks.com. IOW a 24/96 file that is a bit-for-bit copy of the relevant segment of the file originally downloaded from www.hdtracks.com.  It is completely legal and also authorized by HA's TOS  for people to upload short file segements like this. There are already a ton of them here.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #48 –
I've posted a clip [a href='index.php?showtopic=74658']on the parallel upload thread[/a] of one of the softest passages in my music collection, the beginning of the development section in the first movement of Beethoven's Symphony #3 "Eroica".  This is the Minnesota Orchestra again.  It's a BIS hybrid SACD, which means that the CD version is presumably mastered according to current best practices, and also that I can do informal comparisons with a high-resolution version (originally recorded in 24/44.1).  Reviewers faulted the conductor for making this passage so soft.  To me it sounds superb in SACD stereo, and the CD version is still pretty good, though a little less clean and with less sense of ambience.  Looking at a spectrogram, I find that, contrary to my expectations, it is noise-shaped.  The shaped noise completely obliterates any feature above 15 kHz.  I am curious to know whether I could possibly perceive anything above 15 kHz in this soft a context.  If I had access to the 24-bit version, I'd do an ABX with and without a 15 kHz lowpass.  Are there any other plausible explanations of the difference I hear between the two versions?

Also, I'm curious how the noise shaper used at BIS compares to the one on my Audacity.

I've made a version of the Rachmaninov without dither, and when I've had time to compare it to the flat TPDF version I'll report back.

Successful ABX of TPDF white dither vs. noise-shaping at normal listen

Reply #49 –
Thanks for that sample - looking at the spectrogram, I agree, it already seems to have been noise shaped.

[edit] It is also *very* quiet - Replay Gain of +24.66dB. This sample of the track is certainly meant to be listened to at much lower levels than it will be in isolation.[/edit]