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I am developing an app based on soundphrases for android. I record a voice with my samsung galaxy SIII and then use audacity for making the quality better. Then this soundfile is exported as an uncompressed WAVE-file. I compress it to an APE-format with monkeys audio (free opensource) and then convert the ape-format to MP3.

SO my question is - if I want to do something more with these sounfiles - does it matter if I work with the compressed MP3-formats or work with the raw WAVE-file format? Does it deteriorate the quality if I once again open and save the MP3-files? (could be compared with once again opening a jpg pic. in photoshop

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Sound files are not meant to be edited once they've been applied a compression algorithm, audio data compression simply isn't meant to be used like that (for the files to be edited post-compression). The reason is that the result will be to the worse (compressed files have already increased noise floor, lessened frequency content, compromised stereo field...) whereas with the lossless versions you're still utilizing the full depth of the original sound while adding new edits or processing. Also the compression algorithm itself performs differently depending on what it's fed, so you get different compression results with differently modified sound files. That's why you can't e.g. double compress a file without creating unwanted compression "errors" when compressing an already compressed file for the second time (the compression algorithms are meant to be used for lossless audio, always).

It's not recommended to modify compressed files instead of the corresponding uncompressed files, but it can be done.

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  • Normally I use the uncompressed Wave-files but it has occurred that I could not find one and another such raw files. In that case I was forced to take the compressed mp3-format and when I listened I could not hear any deteriorated sound. But Maybe I did not listen enough. And more - the soundfiles are voices of some seconds - approx. 3 seconds. Maybe its another thing with music?
    – Björn Hallström
    Nov 15, 2013 at 23:39
  • Well, in general, use your ears. Many numerical errors that happen in digital audio systems and e.g. file compression are insignificantly small or inaudible (they may be numerically analyzable or known though and thus existing). E.g. most people find MP3s totally listenable, regardless of that they're lower than CD quality.
    – mavavilj
    Nov 16, 2013 at 0:50
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Yes, multiple MP3 encoding passes results in what's called generation loss with each pass. This distortion and loss of fidelity will accumulate every time you encode to MP3, because of the nature of MP3. Yes, this generation loss is perfectly comparable to opening a JPEG in Photoshop multiple times. This is not a problem with lossless formats like WAV, FLAC, APE etc. Yes, if you're going to be doing "something more" with them, you ideally want to work with your original files, or as close to original as you can, if you care about quality.

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  • On an unrelated note, I recommend you try compressing your files with FLAC. I think you'll find similar results to what you get with Monkey's, but in much much less processing time.
    – Jesse P
    Mar 26, 2015 at 20:20

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