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Topic: Compare extracted audio (Read 576 times) previous topic - next topic
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Compare extracted audio

Hi. My first post. I'm not normally a forum type of person. What has happened to me seems worth a query here.

1. I extracted audio from a CD using CueRipper, saved as a wave, audio1.wav.
2. Extracted same audio from same CD with Adobe Audition, audio2.wav.
3. Compared the two and they were different.

Comparing wave files can be pretty tricky. I resorted to inverting audio1 and not audio2, opening both, inverted and non-inverted, in a multitrack session in Audition, and playing them together. Normally when the files are identical, they cancel out – you won't hear anything. Supposing you edited in one file only, the difference should be audible. It is.

In this case neither file was edited. The expected result was silence on playback in multitrack.

Instead there was sound all the way through, distorted, tinny-sounding, no doubt because of the overlap, but definitely the original audio ripped from the CD.

????

I have the following theories.

A) CueRipper or Adobe are lying about losslessness. One might extract losslessly, the other not? (I think we can rule that one out.)
B) The files are not identical because they were extracted and/or saved differently.

Why? How?

Does anyone know?

Re: Compare extracted audio

Reply #1 –
Was read offset correction applied in CUERipper?
korth

Re: Compare extracted audio

Reply #2 –
Never heard of it. The audio did have a 2 second pre-gap in the CueRipper version, which I inserted in the Adobe version.

Note: I don't think the timing was off by even a single sample.

Could you explain "read offset"? Thanks.

Re: Compare extracted audio

Reply #3 –
http://cue.tools/w/images/c/cc/CUERipper_settings_1.png

Item 15 in the above image shows the read offset correction (in samples) that was detected by CUERipper.

See spoon's Audio Guide for an explanation of read offset
https://dbpoweramp.com/spoons-audio-guide-cd-ripping.htm

Edit: When an offset is applied to the ripped audio, samples are removed from one end of the rip and null samples are padded to the other end.
korth

Re: Compare extracted audio

Reply #4 –
Read offset was 6 in CueRipper. Audition does not, to my knowledge, have the setting available, which isn't the same as to say, read offset is not automatically applied, determined by the drive model. (I think.)

I'm going to attach two screenshots of Audition close-up, that let you see samples and time in milliseconds. Bearing in mind that one audio is inverted, the waves look the same. Sorry in advance about the blurry resolution.

The sample at 0:02.306 is where it should be in both files – not displaced. It will take a moment to upload the images to a server. If you want them, they'll be in my next reply. 10-15 minutes.

Re: Compare extracted audio

Reply #5 –
Please send any link to audio files (if that is what you meant) via personal message.
Our terms of service prohibit audio clips over 30 seconds in length.
korth

Re: Compare extracted audio

Reply #6 –
2 jpgs? I can send them by personal link. 1295 x 1211.

Give me a few minutes to figure out how p0ersonal messages work.

Re: Compare extracted audio

Reply #7 –
A CD Image is a term for an audio rip of an entire CD. I edited my previous message that I was referring to audio files. Sorry, I'm at a family gathering and keep getting interrupted.
korth

Re: Compare extracted audio

Reply #8 –
Take your time. Thanks for your suggestions so far.

I sent you a personal message (with jpegs, I hope).

What I'm wondering long term, assuming a difference in the way audio is extracted, ... which is better, CueRipper?

Re: Compare extracted audio

Reply #9 –
See the link I posted earlier to spoon's Audio Guide. CUERipper has Secure Ripping.
It also can compare your rip (if previously ripped and submitted by someone else) to the AccurateRip and CUETools databases.
korth

Re: Compare extracted audio

Reply #10 –
To quote Spoon's Audio Guide:
Quote
Modern CD drives (every drive bar a handful in the last 4 years) support Accurate Stream, this feature allows a CD drive to precisely locate an area of CD

My CD drive might be older than 4 years. Maybe that means it is unpredictable. I can't say.

In Audition, comparing audio extracted twice, by Audition, the two files are the same always. The only difference, and a major one at that, occurs when extracting one audio with Audition and one with CueRipper.

The interface in Audition shows you where samples are. For example, at position 0:02.306. I personally can't see a difference between audio1.wav and audio2.wav sample-wise. My only evidence of a difference is the multitrack playback with one file inverted. It may well be an offset issue, but how to tell?

Adobe unlike CueRipper, I suspect, will not have a forum like this one to ask the question.

As a further test of the "read offset", I could try to align the waves by tweaking them one sample at a time in Audition. I hesitate to do so. A lot of work and possibly for nothing.

Could it be anything else, other than read offset?

Re: Compare extracted audio

Reply #11 –
A CUETools accurip log for each file might reveal something.

If you're familiar with foobar2000 (also on the forums) the files can be compared for differences or offset.
korth

Re: Compare extracted audio

Reply #12 –
I'll try that.

A comparison in Exact Audio Copy (EAC) revealed no differences so far.

Foobar2000 then. To be continued ...

Re: Compare extracted audio

Reply #13 –
Progress. AA has a filter called 'Repair DC Offset'.

Google's AI Overview:
Quote
The DC offset shows any direct current offset that was applied to the waveform during recording. Some sound cards record with a slight DC offset, which can cause the center of the waveform to be offset from the zero point.
You can also repair DC offset issues by going to the favorites menu and selecting Repair DC Offset.

As a general rule, I apply the filter to tracks and images before burning or converting them. Interestingly DC offset is visible in Audition's 'wave view panel' as a vertical displacement from the center, while read offset 'presumably' shows up as a horizontal displacement of the wave.

Since I was working with the original files extracted from CD, I hadn't gotten around to repairing DC offset. Now I  have, and lo and behold, the files match. Not perfectly. Music is still very very faintly audible playing in multitrack with a file inverted. The interesting part is that I only needed to repair DC offset in the Audition generated audio file. CueRipper's audio2.wav file did not require it.

Foobar's 'Bit ocmparison' tool correctly analyzed that audio2 (CueRipper) had a non-zero offset of 6 samples, but then did not detect any notable difference in the files. Comparing again with corrected offset...

Foobar:
Quote
Compared 111396594 samples, with offset of 6.
Discarded 6 trailing null samples from file #1.
Discarded 6 leading samples containing non-null values from file #2.

Again nothing of note.

Repairing DC offset did the trick. The very faintly audible music is perhaps a difference in how CueRipper repairs DC offset.

Problem resolved. Thanks for your time.