Interpreting sampling rate of mp3 files

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I thought mp3 encoding doesn't have a uniform sampling rate, how then sox --i shows sampling rate field for mp3s? I see 44100 sampling rate for an mp3 file.

user13107

Posted 2014-03-15T07:27:20.987

Reputation: 103

1This is a sound design forum, i downvoted your question because it's off topic and can by answerred easily by a google/wikipedia search. – Arnoud Traa – 2014-03-15T07:50:16.103

@ArnoudTraa then the URL should have been sound-design.SE no? Why call it sound.SE? – user13107 – 2014-03-15T07:52:58.887

1Relax, i didn't create that name. This used to be called 'social sound design' not my decision to change that. But did you look at wikipedia for samplerate and mp3 bitrates? – Arnoud Traa – 2014-03-15T08:30:56.360

Oh btw i see now that the site actually does say Sound Design :) It's just not in the URL. – Arnoud Traa – 2014-03-15T11:04:11.133

@arnoudtraa - because it is the combination of the audio-production and social sound design sites and having to type sounddesign.stackexchange.com is far longer when there is no other sound sites. – AJ Henderson – 2014-03-17T13:58:19.877

ok i understand, but it explains the confusion :) – Arnoud Traa – 2014-03-17T16:58:24.787

2I'm voting to close this question as off-topic because it's not useful or a good fit. – None – 2016-10-07T04:47:09.743

Answers

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Simply, your understanding is incorrect. MP3 does use a uniform sampling rate, it reduces resolution of the sound in areas where the resolution is unneeded so that it fits a simpler pattern that can be more efficiently compressed, but it decodes to a fixed sample rate.

As EMV was kind enough to point out, you may be thinking of the bitrate. The bit rate is the amount of data that it takes to encode those samples. Since resolution is selectively dropped, the amount of data required to store each sample is variable and thus the actual data rate will vary, even though the sampling frequency itself does not.

I suggest the Wikipedia page on MP3 for further reading.

AJ Henderson

Posted 2014-03-15T07:27:20.987

Reputation: 7 961

1To add to that: you're maybe confusing sample rate (constant) with bitrate (not necessarily constant: there are cbr and vbr mp3 files). – EMV – 2014-03-17T14:16:12.897

@EMV - great thought on why they may be getting confused. – AJ Henderson – 2014-03-17T14:24:57.503