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I have two audio files in wav format, one of them has some noise because I have modified some bits inside the file. I can just play those files using audio player and other people could hear the difference. But I must also represent it using graphics to show them that two files are not same.
What technique/method do I need to achieve that? And is there any free/cheap software to do that?
When no specific feature is to be observed in sound, the best way to represent it is to display its spectrogram since it reflects what the ear does: measuring energy among frequencies as its varies with time.
You can get that representation using the free and open source command-line tool SoX:
sox sound-original.wav -n spectrogram -o sound-original.png
sox sound-altered.wav -n spectrogram -o sound-altered.png
The alterations in the second sound can clearly be seen on its spectrogram which is good.
But in the case of more subtle alterations, it could be difficulty to see them.
In such a case, computing the difference between the two signals and displaying its spectrogram would be appropriate:
sox -m -v 1 sound-original.wav -v -1 sound-altered.wav sound-difference.wav
sox sound-difference.wav -n spectrogram -o sound-difference.png
Alternatively, creating the spectrogram directly without writing a temporary file:
sox -m -v 1 sound-original.wav -v -1 sound-altered.wav -n spectrogram -o sound-difference.png
In the command above, -m asks SoX to mix audio files together, and -v is intended to change the volume by a linear factor.
In our case, the volume of sound-original.wav is left unchanged, whereas the -1 factor applied to sound-altered.wav is used to invert it.
The whole command computes the difference between the two audio signals.
Sonic Lineup is a very nice interactive GUI tool for comparing two (or more!) audio files. It's open-source, cross-platform (Windows/Linux/Mac), written in C++ and Qt, and it automatically aligns each audio section. Then, you can start playing and switch between each audio file at any time.
Look at this screenshot! We can clearly see that this section was longer (8 seconds longer) in the second file. Given these are 26-minute long files, it would be very hard to find this difference otherwise.
Any DAW will create a valid visual representation of any given waveform. You can search for a free one. I can hardly understand the reason though..
It depends on what changes you have made really, what kind of analysis would show the difference depends on this.
If you just want simple waveform displays then Audacity is the go-to open source multitrack recorder/editor.
If you want a more thourough and detailed screenshot, something like iZotope Insight (VST) would probably be my choice. You can feed the two separate channels into it and overlay them in a 3D spectrogram for example.
I think the trial version should allow you to do this if you just want to get a screenshot.
Also, you could subtract one file from the other to get a waveform (or other) display of just the difference if you wish to.
There are many ways to display the two files to show the difference, as I said at the start, it depends on what you need people to see.
