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help/opinons on multiple speed change quality - test
bomber1978
post Sep 24 2013, 11:57
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Hello,
I'm not sure if I can post this here, or if anyone will be interested to help/give their opinion, I guess it can just be ignored if you're not interested to help...
I have been testing various programmes "speed change" function quality , as I have been pretty seriously correcting analog cassette tape live recordings speed...
In testing the quality of the "speed change" function I took an original file off a CD and changed the speed 9 times (yes I know that's an extreme amount but I wanted to push the test to the limits!).
The original file is 7min:9secs.26667 (5 decimals is the most I can see, beyond that I don't know...), after changing the speed of the original file 9 times I returned it to the original length of 7min9secs.26667, I then created a mixdown of the original file and speed changed file, as the mixdown cancels out audio which is the same so you can hear any difference between the 2 files....
By ear doing ABX type tests I can not hear any difference between the original file and the 9 times speed changed file (I keep thinking I can but blind tests have proven me wrong many more times than I was right!). So I created the mixdown, however I'm not sure if the mixdown results are accurate, because the mixdown starts off at a low volume and gets louder as the track lengthens, so I think this could be because of time lag, I'm guessing it's because the file time length doesn't match somewhere after the 5th decimal spot which I can not see..., I know the difference the mixdown is showing could possibly be digital noise because of bad quality speed change, but the fact the mixdown starts off at a low volume and gets louder seems to indicate to me that it's more of a time lag problem (I really don't know for sure which is why I'm asking for opinion here!).
I am hoping someone with much better knowledge than me (probably most people here!) would be able to please take a listen to my files, and please let me know your opinion, that would be greatly appreciated! I'm sure there has to be some time lag, but more importantly I'm wondering if anyone can hear any real difference in quality between the original file and speed changed 9 file?, as the purpose of my test is to test the quality of the speed changed file against the original...

The following 3 files can be downloaded here:
ORIGINAL FILE:
http://www.sendspace.com/file/smrrdv

SPEED CHANGED 9 TIMES FILE:
http://www.sendspace.com/file/9idl1n

MIXDOWN of original file and speed changed 9 times file:
http://www.sendspace.com/file/6380gy





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bandpass
post Sep 24 2013, 16:50
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Audacity 2.0.3 uses the SoX algorithm (however, the change-speed dialogue box erroneously refers to libsamplerate). Assuming default settings, this means this graph from the src comparisons site applies:



The noise floor (faint blue) is that of 32-bit floats. Speeding up then down by a few % gives a slight hi-freq roll-off, but I doubt very much that it's audible; you could probably perform the conversion many 1000s of times and still not hear a difference.
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bomber1978
post Sep 24 2013, 18:17
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QUOTE (bandpass @ Sep 25 2013, 01:50) *
Audacity 2.0.3 uses the SoX algorithm (however, the change-speed dialogue box erroneously refers to libsamplerate). Assuming default settings, this means this graph from the src comparisons site applies:



The noise floor (faint blue) is that of 32-bit floats. Speeding up then down by a few % gives a slight hi-freq roll-off, but I doubt very much that it's audible; you could probably perform the conversion many 1000s of times and still not hear a difference.


So it uses SoX even though it says it uses libsamplerate?
Can you tell what both Audacity 1.2.6 and 2.0 used?, as I've used them also...
Thanks
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uart
post Sep 24 2013, 19:29
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QUOTE (bomber1978 @ Sep 24 2013, 10:17) *
So it uses SoX even though it says it uses libsamplerate?
Can you tell what both Audacity 1.2.6 and 2.0 used?, as I've used them also...
Thanks

Unfortunately earlier versions were significantly worse. Looking at the results HERE version 2.0 appears to be "broken".

This post has been edited by uart: Sep 24 2013, 19:29
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bomber1978
post Sep 25 2013, 06:06
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QUOTE (uart @ Sep 25 2013, 04:29) *
QUOTE (bomber1978 @ Sep 24 2013, 10:17) *
So it uses SoX even though it says it uses libsamplerate?
Can you tell what both Audacity 1.2.6 and 2.0 used?, as I've used them also...
Thanks

Unfortunately earlier versions were significantly worse. Looking at the results HERE version 2.0 appears to be "broken".


Hi,
I can't tell what that graph for Audacity 2.0 exactly means (the one you say appears to be "broken").
I have been using it (2.0) for the past year, are the results you have seen relating to 2.0 something which would be audible?
Thanks
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uart
post Sep 25 2013, 13:12
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QUOTE (bomber1978 @ Sep 24 2013, 22:06) *
QUOTE (uart @ Sep 25 2013, 04:29) *
QUOTE (bomber1978 @ Sep 24 2013, 10:17) *
So it uses SoX even though it says it uses libsamplerate?
Can you tell what both Audacity 1.2.6 and 2.0 used?, as I've used them also...
Thanks

Unfortunately earlier versions were significantly worse. Looking at the results HERE version 2.0 appears to be "broken".


Hi,
I can't tell what that graph for Audacity 2.0 exactly means (the one you say appears to be "broken").

Go to that link and select "Audacity 2.0 (High Quality)" in the converter drop down and compare (leave the test set to sweep). All the purple and red stuff that you can see there (other than the main white trace) is essentially distortion - as in harmonic components that shouldn't be there.

QUOTE
I have been using it (2.0) for the past year, are the results you have seen relating to 2.0 something which would be audible?

By "broken" I only meant that it is significantly worse than other contemporary sample rate converters. As bandpass points out, it's still probably inaudible at about -80 dB. The best resamplers however have those harmonic levels down around -140 to -150 dB level (pretty much consistent with 24 bit digital silence). With levels like that you don't even attempt any kind of listening test, because you know it's futile.

This post has been edited by uart: Sep 25 2013, 13:14
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bomber1978
post Sep 25 2013, 13:31
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Agh I think I just wasted my time, when you said it was "broken" I thought you meant there would be audible quality loss, so I changed a file 9 times with 1.2.6 and loaded it onto my desktop with 2 of the original files and tried 20 times to pick the odd one out (the speed changed file), I got it correct 7/20 times so I guess nothing definitive there.... However results were completely different when I set quality from "HQ" to "fast sync", I got it right 10/10.

This post has been edited by db1989: Sep 25 2013, 18:57
Reason for edit: deleting pointless full quote of above post
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Posts in this topic
- bomber1978   help/opinons on multiple speed change quality - test   Sep 24 2013, 11:57
- - pdq   I'm sure this is obvious, but if you can't...   Sep 24 2013, 12:48
|- - bomber1978   QUOTE (pdq @ Sep 24 2013, 21:48) I'm ...   Sep 24 2013, 13:19
|- - Arnold B. Krueger   QUOTE (bomber1978 @ Sep 24 2013, 08:19) Q...   Sep 24 2013, 22:00
- - bandpass   Bear in mind that changing speed digitally is impl...   Sep 24 2013, 13:35
|- - bomber1978   QUOTE (bandpass @ Sep 24 2013, 22:35) Bea...   Sep 24 2013, 13:40
- - Arnold B. Krueger   There are at least 2 different ways to change the ...   Sep 24 2013, 13:37
|- - bomber1978   QUOTE (Arnold B. Krueger @ Sep 24 2013, 22...   Sep 24 2013, 13:44
|- - saratoga   QUOTE (bomber1978 @ Sep 24 2013, 08:44) N...   Sep 24 2013, 15:39
|- - bomber1978   QUOTE (saratoga @ Sep 25 2013, 00:39) QUO...   Sep 24 2013, 15:58
|- - Arnold B. Krueger   QUOTE (bomber1978 @ Sep 24 2013, 10:58) Q...   Sep 24 2013, 17:59
|- - bomber1978   I think that is refering to "change pitch...   Sep 24 2013, 18:10
- - bandpass   Audacity 2.0.3 uses the SoX algorithm (however, th...   Sep 24 2013, 16:50
|- - bomber1978   Hi, I actually didn't use the default in Audac...   Sep 24 2013, 17:13
||- - bandpass   QUOTE (bomber1978 @ Sep 24 2013, 17:13) I...   Sep 25 2013, 08:08
|- - bomber1978   QUOTE (bandpass @ Sep 25 2013, 01:50) Aud...   Sep 24 2013, 18:17
|- - uart   QUOTE (bomber1978 @ Sep 24 2013, 10:17) S...   Sep 24 2013, 19:29
||- - bomber1978   QUOTE (uart @ Sep 25 2013, 04:29) QUOTE (...   Sep 25 2013, 06:06
||- - uart   QUOTE (bomber1978 @ Sep 24 2013, 22:06) Q...   Sep 25 2013, 13:12
||- - bomber1978   Agh I think I just wasted my time, when you said i...   Sep 25 2013, 13:31
|- - bandpass   QUOTE (bomber1978 @ Sep 24 2013, 18:17) S...   Sep 24 2013, 20:21
- - bandpass   It's all about likelihood: the more distortion...   Sep 25 2013, 07:15
- - Juha   Have you tried alternative software for your SRC t...   Sep 25 2013, 07:28


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