I'm looking to convert some audio files into spectrograms. I'm wondering what the difference is between an m4a and wav file. If I have two of the same audio recording, one saved as wav and the other as m4a, will there be a difference in the spectrogram representations of both?
12 Answers
Both WAV and M4A are container formats, with options for how exactly audio data is encoded and represented inside the file. WAV file has one audio track with variety of encoding options including those possible for M4A format. However most often typically WAV refers to having uncompressed audio inside, where data is contained in PCM format.
M4A files are MP4 (MPEG-4 Part 14) files with an implication that there is one audio track inside. There are much less encoding options even though they still include both compressed and uncompressed ones. Most often M4A has audio encoded with AAC encoding, which is a lossy encoding. Depending on that loss, roughly on how much of information was lost during the encoding, your spectrogram could be different from the one built on original data.
The m4a format uses a lossy compression algorithm, so there may be differences, depending on compression level, and the resolution and depth of the spectrogram. The .wav format can also be lossy, due to quantization of the sound by an A/D or any sample format/rate conversions. So the difference may be in the noise floor, or in the portions of the sound's spectrum that are usually inaudible (due to masking effects and etc.) to humans.
