[khaos974]

It's called Audio DiffMaker, available at http://www.libinst.com/Audio DiffMaker.htm
 
Basically, it allows you to compare 2 audio files easily, time alignment, volume matching... is done automatically.
The process is called nulling, determining the difference between two audio signals via subtracting the 2 tracks.
the reason it works is that when recording the 2 signals with the same recording device, the difference due to the A/D conversion disappears in the nulling process, the only thing left is the difference between the 2 played signals.
But since the author of this little piece of software can explain much better than me, here he goes:
 
Audio DiffMaker is a freeware tool set intended to help determine the absolute difference between two audio recordings, while neglecting differences due to level difference, time synchronization, or simple linear frequency responses.
 
The difference recording  that results is only what has changed between the two recordings.  If anything - a change of component, a treatment, mechanical damping, etc. - is having any audible effect on the audio signal in a system, the difference recording will have audible content. The end result is primarily intended to be evaluated by ear.
 
 
What Can Audio DiffMaker Do?

Some of the tools within Audio DiffMaker can be used to:

1. Precisely align two similar audio tracks to the same gain levels and timing
2. Extract and listen to even very tiny differences between pairs of audio tracks
3. Quickly compare two or more recorded audio signals under precisely gain-matched and time-matched conditions.
4. Measure the frequency response of the equipment being tested and apply it so the effects of linear frequency response can be removed from the testing.  
5. Record sounds at various sample rates and bit resolutions up to 24bit/192kHz with the "Recorder" tool.
6. Select and copy sections of audio tracks, trim them, or "rip" them from audio CDs, with the "Trimmer/Ripper" tool.
7. Quickly see the responses of devices or entire audio systems (even rooms) using the included high resolution 1/6th octave frequency/spectrum "Response Analyzer" and matched pink noise source. 
8. Compact multiple WAV files, and a text description, into one easily transported "DYF" file.  Just double-click on a DYF file in Explorer and Audio DiffMaker will open and load the files, ready for listening.

 
 

 

[Trysaeder]

Why do they have to use .wav? It's very annoying.

 

[khaos974]

No love for a new testing tool?
Not interested in knowing if you can hear a -70 dB difference?
 
Which is what I actually tested:

1. V5 mp3 ~130 kbps were compared to  the original file and the null was around -50 dB.
2. V0 mp3 ~245 kbps were compared to  the original file and the null was around -70 dB.

 

[Roger Strummer]

Hadn't seen this thread... the tool seems really useful, I'll use it in some tests comparing adc's and report the difference. Thanks for posting it! 

 

[jcx]

lossey codecs aren't the natural thing to test this way - they are busy throwing out masked frequency components so may be > 10 % different from their full rate source - its nice to know they make similar decisions on what to keep but it DiffMaker really isn't a psychoacoustic coding investigation tool
 
the more expected use would be looking at purportedly flat channel/signal chain components like amplifer differnces

 

[khaos974]

That's why you can listen to the difference to see what was thrown away, I do agree that it's net the best way to test psychoacoustic model though.
 
Quote:

lossey codecs aren't the natural thing to test this way - they are busy throwing out masked frequency components so may be > 10 % different from their full rate source - its nice to know they make similar decisions on what to keep but it DiffMaker really isn't a psychoacoustic coding investigation tool
 
the more expected use would be looking at purportedly flat channel/signal chain components like amplifer differnces

 

[Roger Strummer]

Although jcx is right, it can be somewhat useful for comparing lossy codecs between them as in how much the original signal is altered, because the result you get from comparing the lossy and lossless version can be seen as an upper bound for the difference that a person will perceive between the files.
 
But yeah, the main use I see for the tool is for comparing components. I believe it can really put in perspective the law of diminishing returns (my hypothesis for example is that the difference between an onboard dac and a entry to mid level external dac will be FAR greater than the difference between said external dac and an ultra high end one).

 

[Trysaeder]

How do you compare non wav files? I can't seem to change the 'reference' track.

 

[Roger Strummer]

The trick would be to convert the lossy files (or any file for that matter) to wav files, I think you were right that it only supports wav files.