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16 bit vs 24 bit, any samples that work?
AndyH-ha
post Nov 3 2006, 03:19
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There are real differences between 16 bit and 24 bit files, just as there are real differences between uncompressed and mp3. As with the differences between wav and mp3, 16 bit vs 24 bit is often difficult to identify by listening.

Test signals are one thing, but has anyone found any 24 bit music recording that can be successfully identified via ABX testing against a properly resample to 16 bit version of same?
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saratoga
post Nov 3 2006, 03:25
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I'd imagine ABX would be possible if you found a sample with a near silent portition in the middle and listened with the volume cranked up uncomfortably loud. The 16 bit version should have noise down at ~-100dB. Assuming your equipment was good enough, the room quiet enough, and you didn't deafen yourself on the preceeding section (all big assumptions), you could probably ABX it.
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pdq
post Nov 3 2006, 05:33
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I recall a test here some years back to try to see if people could ABX a 16-bit original from the same clip reduced to 15- 14- and 12-bit depth with proper dithering. The result was that very few people could ABX the 15-bit file (only one as I recall) and many could not ABX the 12-bit file. Being able to distinguish 24-bit from 16-bit should be even more difficult.
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Aetmos
post Nov 3 2006, 06:22
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If the clip is properly dithered, this doesn't really prove much of anything other than the dithering did its job. The whole point of dithering is to make the resultant 16-bit file sound as much like the 24-bit version as possible. A better real-world test would be to record two different multi-track sessions, one in 16 bit and one in 24 bit. You would still have to dither the final mixes, but the difference, especially if there was some degree of processing, should be quite distinguishable.

QUOTE
As with the differences between wav and mp3, 16 bit vs 24 bit is often difficult to identify by listening.


Really? With a good set of speakers, I think most mp3's are relatively easy to identify...

This post has been edited by Aetmos: Nov 3 2006, 06:27
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cabbagerat
post Nov 3 2006, 07:31
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QUOTE (Aetmos @ Nov 2 2006, 21:22) *
If the clip is properly dithered, this doesn't really prove much of anything other than the dithering did its job. The whole point of dithering is to make the resultant 16-bit file sound as much like the 24-bit version as possible. A better real-world test would be to record two different multi-track sessions, one in 16 bit and one in 24 bit. You would still have to dither the final mixes, but the difference, especially if there was some degree of processing, should be quite distinguishable.
Very few people question that 24bit is superior to 16bit for mastering and processing purposes. The question is really whether it's useful to distribute content to the customer in 24bit over 16bit. Dithering a 24bit signal down to 16bit is, in my opinion, the right approach to make samples to test the hypothesis that end-users need 24bit formats.

QUOTE (Aetmos @ Nov 2 2006, 21:22) *
QUOTE
As with the differences between wav and mp3, 16 bit vs 24 bit is often difficult to identify by listening.


Really? With a good set of speakers, I think most mp3's are relatively easy to identify...
Welcome to HA. I see this is your first post. Can I suggest that you read the Terms of Service, especially number 8. If you do indeed find the majority of mp3s easy to identify in a proper double blind test, then you should contribute to some of the encoder development and testing that goes on around here.

Andy: Can I suggest a classical sample like Ravel's Bolero or Copland's Appalacian Spring - a good recording of both are very dynamic with very quiet sections and very loud sections. I have tried 16 versus 24 before and failed, but I think samples like these might be useful.


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AndyH-ha
post Nov 3 2006, 09:36
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I agree that a good sample, if it exist in music, would be something that has very low level passages, perhaps one or both of those suggested. Unfortunately I have nothing of that sort on which to test. The only sources I have to record at 24 bit are already existing recordings on vinyl, tape, and CD. Those are not good candidates for the obvious reasons. The differences exist at every signal level of course, even from a CD going D to A followed by A to D, but detecting those differences with human hearing is the task.

Just to reiterate, this post is not about theory. It is an inquiry about what people have experienced. Has anyone been able to do a valid ABX test? Is so, on what?

This post has been edited by AndyH-ha: Nov 3 2006, 09:38
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Aetmos
post Nov 3 2006, 16:17
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QUOTE
Welcome to HA. I see this is your first post. Can I suggest that you read the Terms of Service, especially number 8.


Ah, sorry about that. No, I've not participated in any double-blind studies.

QUOTE
If you do indeed find the majority of mp3s easy to identify in a proper double blind test, then you should contribute to some of the encoder development and testing that goes on around here.


I'd be happy to.

QUOTE
The only sources I have to record at 24 bit are already existing recordings on vinyl, tape, and CD. Those are not good candidates for the obvious reasons.


Why not record a musical selection from a CD that does not have a wide dynamic range (i.e. rock / electronica / contemporary jazz), but record it peaking at around -24dB? It's not an ideal solution, but if those three are your only sources, it would minimize the effect of the original recording being at 16 bit, because (I believe) 16bit and 24bit have been shown to be fairly indistinguishable at high recorded levels. Alternately, just recording an acoustic guitar or a piano at 24bit seems like it would be a reasonably good source.

Anywho, hope I haven't stepped on any (more) toes...

Tom

This post has been edited by Aetmos: Nov 3 2006, 16:27
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cabbagerat
post Nov 3 2006, 16:25
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QUOTE (AndyH-ha @ Nov 3 2006, 00:36) *
Just to reiterate, this post is not about theory. It is an inquiry about what people have experienced. Has anyone been able to do a valid ABX test? Is so, on what?
I know negative results aren't what you are looking for, but I have spent a while trying this on native 24bit material and failed. This is probably due to one of two things. First, my listening environment isn't very quiet. My PC is extremely quiet and I use good headphones, but the traffic noise from the nearby road is still audible. Second, a large amount of 'native' 24 bit material I have come across doesn't have a better noise floor than properly dithered 16bit material - that is, the noise floor is above quantization noise.

It would be pretty cool if somebody could point us towards a real 24bit recording with a noise floor of less than, say, -100dB.


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Axon
post Nov 3 2006, 17:48
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I suppose it's quite easy to construct a track with very low-level musical content, with very high-level transients, so that the steady-state content is 80-100db below the transient peak. However, for that to work, you'd need to ABX quantization noise in a signal that is perhaps only 20-30db in volume. Still quite hard, you'd need IEMs with good noise isolation, but certainly possible. The transient, obviously, needs to be short enough not to cause permanent damage.

Oh oh oh - another idea. Dump all the high-amplitude energy into low frequencies. Think of the infamous cannon shot in Teldec's 1812 Overture LP. You'd need a sub for that, but it would probably avoid the more pressing issues of ear damage.
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Axon
post Nov 3 2006, 18:03
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Also, how contrived can the listening environment get? Would it be reasonable to use a compressor in the playback chain?
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AndyH-ha
post Nov 3 2006, 20:18
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The question isn't whether or not it is possible to distinguish something in 24 bit vs 16 bit, although that is a challenge in itself, but to distinguish some music. Can it ever make a difference with music?

For instance, using a test tone, it is fairly easy to demonstrate the difference between converting from 32 bit to 16 bit with dithering vs no dithering, but doing the same thing with real music is more problematic.

Also, in my test tone trials, I can easily enough hear the difference between dithered and undithered 16 bit, but even under these simplified conditions, not between 32 bit and dithered 16 bit. Those differences are easy to see on screen and to measure, however.
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Axon
post Nov 3 2006, 20:38
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Well.. how much dynamic range can you coax out of a close-mic'd drum? Virtually any drum you hear on any recording is either heavily compresser or not recorded in the nearfield.
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AndyH-ha
post Nov 3 2006, 21:21
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I'm sorry, that went over my head. What is the relevance to the search for some music recording that has audible differences between 16 bit and 24 bit?
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outscape
post Nov 3 2006, 22:23
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haha nothing.. see 24 bits is purist technology. it is in theory suppose to provide more resolution and hence better sound quality but at the same time there are other factors to consider during playback, such as DACs, the speakers, the listening room/environment, etc. plus even if you COULD abx between 16 bits and 24 bits i doubt that the difference will be that big to fuss about. with today's advanced dithering systems such as pow-r, waves idr etc. and plus given how most music is mastered these days, loud and proud, you won't hear a difference on your consumer level equipment, maybe a slight difference on a very audiophile setup if your hearing ability is that good. and i mean BLIND tests.


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greynol
post Nov 3 2006, 22:41
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I'd wager that in order to distinguish the difference, you'd damage your hearing.

In the spirit of ABX testing aren't you supposed to listen at a comfortable level without aggressively adjusting the volume or eq? IOW, isn't it unrealistic to crank the level while listening to quiet passages just to see if you can hear a difference in the noise floor?


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Axon
post Nov 4 2006, 01:11
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OSHA's recommendations for 120db is that it should not be listened to for over 7.5 minutes, and the recommended exposure time halves for every 5db increase. So, you'd figure that for 1 minute of exposure time, you could go as far as 135db. But obviously very few headphones could even go that far safely, and the OSHA figures are only a model. But I see nothing wrong with a single 120db transient as part of an ABX testable wave file. The biggest problem might be that temporary hearing thresholds can change by 10-20 db the first time you hear it, so it might take several minutes between tests for your ears to cool down.
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AndyH-ha
post Nov 4 2006, 01:56
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But are you talking about real music or, effectively, just a test signal? Even a verified test signal would be something, considering my experience with test signals, but I don't understand the loud part. It seems that only something of very low signal level is likely to be distinguishable -- if anything is. I'm think I'm missing your point completely.
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Axon
post Nov 4 2006, 02:21
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My point is that you don't need a "test signal" to do this, and that if you limit the discussion of wide dynamic ranges to percussion, one can think up a plausible scenario where such dynamic range is necessary to capture something. Think of any musical instrument capable of 120db of measurable dynamic range, and there you go. Or, alternatively, you only need 100db, or 80db, or however much you need while still being able to hear the quantization noise.
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AndyH-ha
post Nov 4 2006, 04:09
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OK, you need more than the dynamic range of 16 bit to faithfully capture the analogue. Easy enough to understand. Then the test can be made. Do a proper resample to 16 bit with noise shaped dither -- or not noise shaped if you have some (strange) idea that will be better. Compare the two.

Of course, the question is still open. Can anyone find or make such a recording that can be successfully ABXed? If you choose your dither carefully, especially without noise shaping, that alone could differentiate the two, but properly done (single pass) noise shaped dither isn't very audible.

With a test tone, I can hear the quantizing noise at the end of a fade when the resample to 16 bit is not dithered but I cannot hear anything at the same point when I dither. With CoolEdit's Statistics I measure Peak -94dB, RMS Average -96dB on the undithered (can hear; at high volume level, of course) vs Peak -77, RMS Average -89dB dithered (can not hear). These numbers compare with Peak -150, RMS Average -161 on the original 32 bit file. Go figure.
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Iain
post Nov 12 2006, 17:14
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I think the best volume for the test would be 'normal' listening levels. Low level signals have less bits to respresent them. If you only listen to low level signals at higher volumes then you aren't really comparing 16-bit- to 24-bit. You may be comparing 10-bit to 18-bit.

Also, most analogue equipment has a noise floor significantly higher than a pure 24-bit noise floor. And, when recording, some of the additional dynamic range (gained from more bits) is used for headroom so that actual amount of bits used for the recording may be as low as 21 or 22.

I would suggest, therefore, it is impossible to realise true 24-bit performance from an actual recording.
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AndyH-ha
post Nov 12 2006, 19:23
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Without cryogenic cooling the intrinsic noise of electronics puts the useable limit at about 20 bits, maybe 19. This is a great deal more resolution than 16 bits can provide directly. Properly dithered 16 bit can approach that but at a higher noise level.

I think many of us are fairly well convinced there is nothing to gain from a greater bit depth on playback. Recording, mixing and mastering is a different question not being addressed here. However, there are a fair number of people out there who are convinced that 24 bit systems sound "so much better." The challenge is to find some evidence; to produce any 24 bit recording that at least one person can objectively differentiate from a properly dithered 16 bit version of same.

If someone can tell them apart, it isn't necessarily because of the greater resolution of very low level detail. There are other measurable differences. The best evidence seems to be that those differences just are not perceptible to humans.
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SebastianG
post Nov 13 2006, 13:30
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I think it's a good idea to mention the importance of the sampling rate when we talk about the audibility of quantization noise. For example you can use a 16/96 setup to get a similar SNR performance compared to 24/48 in the audible frequency range (by use of clever noise shaping filters) plus a flat response upto 40 kHz. In this case 16 bit would be more than enough for distribution.

Even a simple 4th order IIR filter can lower the noise floor about 20 dB below 0.4 times the nyquist frequency -- in case of 96 kHz that'd translate to a 20 dB increase of the dynamic range below 19,2 kHz (and a 20 dB decrease above 28.8 kHz but that shouldn't bother anyone)

This post has been edited by SebastianG: Nov 13 2006, 13:39
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AndyH-ha
post Nov 14 2006, 03:43
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QUOTE
I think it's a good idea to mention the importance of the sampling rate when we talk about the audibility of quantization noise. For example you can use a 16/96 setup to get a similar SNR performance compared to 24/48 in the audible frequency range (by use of clever noise shaping filters) plus a flat response upto 40 kHz. In this case 16 bit would be more than enough for distribution.
First you would have to demonstrate the audibility of quantization noise in 16 bit/44.1kHz stuff to find any excuse to go to a higher sampling rate. Such can be demonstrated in test situations, i.e. simple test tones at very low levels -- but only if the 16 bit file is undithered.

If dithering is used, the quantization noise is not audible. If rational noise shaping is used (it may be clever but it is quite ordinary in digital audio), even the dither is unlikely to be heard. For me, and I suspect for most people, 16 bit, dithered and noise shaped, cannot be differentiated from 32 bit under ABX test conditions (at 44.1kHz) even with simple test tones.

Maybe things would be slightly different under exceptional conditions of no external noise and extremely low noise analogue electronics, but has that been demonstrated? Going to a higher sample rate would move the shaped noise to a still higher frequency, and therefore further frrom the audible band, but would hardly be worth the markedly increased storage cost if it in fact, as is likely, has no audible benefit.

QUOTE
Even a simple 4th order IIR filter can lower the noise floor about 20 dB below 0.4 times the nyquist frequency -- in case of 96 kHz that'd translate to a 20 dB increase of the dynamic range below 19,2 kHz (and a 20 dB decrease above 28.8 kHz but that shouldn't bother anyone)
I don't know what you are writing about. What are the parameters of such a filter (filter variety, cutoff, highpass/lowpass/band pass/, transition bandwidth, etc)? What is it filtering out? Is it hardware or software? Where might it be employed? If it does something useful, why is it not in normal use?
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SebastianG
post Nov 15 2006, 14:16
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QUOTE (AndyH-ha @ Nov 14 2006, 03:43) *
First you would have to demonstrate the audibility of quantization noise in 16 bit/44.1kHz stuff to find any excuse to go to a higher sampling rate.

I don't have to do anything. I didn't claim that higher sampling rates are needed -- just that lower sample resolutions can be used at higher sampling rates to get the same SNR performance in the audible band. I commented because everyone was only talking about bits/sample and not about samples/second. That's all.

QUOTE (AndyH-ha @ Nov 14 2006, 03:43) *
QUOTE
Even a simple 4th order IIR filter ...
I don't know what you are writing about. What are the parameters of such a filter (filter variety, cutoff, highpass/lowpass/band pass/, transition bandwidth, etc)? What is it filtering out? Is it hardware or software? Where might it be employed? If it does something useful, why is it not in normal use?

I'm talking about noise shaping filters. These filters are usually applied in conjunction with dithering while a signal is requantized in software (ie from 24 to 16 bits) to shape the quantization noise spectrally. See this thread, download noise.zip and checkout the sym20.sos filter. If you feel like plotting its response in Matlab: Here's what you should do:
CODE
sos = [ 1.0  -0.6160081826103387  0.7225  1.0  0.8253356149096804  0.25
        1.0  -0.8253356149096804  0.25  1.0  0.6160081826103387  0.7225 ];
[b,a] = sos2tf(sos);
freqz(b,a);

This is a screenshot of the filter design tool showing the filter's response on a logarithmic amplitude scale (Y-axis, each horizontal line = 10 dB, the bright line correspondes to 0 dB) and linear frequency axis (X-axis, 0..nyguist frequency). If you requantize 24/96 to 16/96 using this filter you can still have a SNR of above 110 dB below 19 kHz -- not just 90 dB. If you use the sym30.sos filter instead you can go down to 12 bits/sample and have an SNR of 102 dB below 19 kHz and the PCM data rate would be equal to the rate you need for 24/48.

Cheers!
Sebastian

This post has been edited by SebastianG: Nov 15 2006, 14:40
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SirChristof
post Feb 15 2007, 09:40
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If you have decent equipment and a quiet environment, it should be easy for you to distinguish this test file I created (source 48khz, 24-bit) to a 16-bit conversion.

It's 5 seconds long, and under 100KB. Very low-level pure tone(sine wave) @ 3.5khz (since this is where our hearing is most sensitive).

Test Tone File(48/24)

Convert it to 16-bit using any method you choose, any dither type of any level, I could abx it easily. I have already tried using at least a few dozen combinations of noise shaping and dither levels, along with no dithering (which obviously sounds worse). Always ABX'able. When properly dithered, the tone is still audible at 16-bit, but the noise floor is much worse and the tone becomes more difficult to distinguish from the noise (where it sounds fine at 24-bit).

You need fairly high output levels to do this, but since the file contains no peaks or anything that would resemble "loud", you wont risk damaging your hearing or equipment so long as no other "computer sounds" play during testing.

[Edit: If anyone prefers, here is a 44.1khz version of the same file, created fresh, not via SRC]
Test Tone File(44.1/24)

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