Mp3 and sample rates

Discussion in 'Converters / Interfaces' started by mallardduckman, Mar 7, 2011.

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  1. mallardduckman

    mallardduckman Active Member

    Oct 1, 2004

    So here's a question that's been bugging me for some time. Say I have a song I've recorded in 48k, I bounce it (mixdown) to both a wav and an mp3, without downsampling to 44.1 so I can maintain as much quality for mastering.

    I understand that the wav file is 48k, and if my clock is set to 44.1 on my rig then it will play back strangely, sped up, as it should. But..the mp3 plays back perfectly in quicktime or itunes, regardless of my rig's clocked rate. This leads me to believe that sample rates don't effect mp3s at all.

    However, I gave a client of mine an mp3 of her mix(48k) to upload to a website for streaming playback. The 48k version of the song would not play. How strange! So I went back into my DAW, rebounced and downsampled the mix 44.1k and then created an mp3 of that. Now it works! So this leads me to believe that sample rates do in fact effect mp3s!

    Which one is it? Does the sample rate of an audio file (wav or aiff) effect it's encoded mp3? If so, how? ..and why on earth doesn't any mp3 converter (itunes, switch etc.) ask if the sample rate should be changed to 44.1?

    Keep in mind I'm not at discussing bit rates like 128, 192, 320 etc., unless bit rates have something to do with sample rates in mp3s.


  2. Boswell

    Boswell Moderator Distinguished Member

    Apr 19, 2006
    Home Page:
    MP3s are not restricted to a particular sample rate, and have the basic rate used encoded in their header as well as the bit rate of the particular encoding. Some equipment will auto-adjust to 48K or whatever basic rate is encoded and the MP3 will play correctly, whereas other gear may be more exacting. It's likely that the website you mention will only accept 44.1K as an original rate and not play any MP3 encoded with other rates in its header.

    By the way, forcing the 48K file to play at 44.1K will result in it playing slower rather than sped up.

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