| From: | Alastair M. Robinson |
| Date: | 5 Aug 2000 at 00:55:55 |
| Subject: | Re: Mpeg 3 playback. |
Hi Everyone,
>> By the way, are you sure that mp3's are saved as 16 bit, or any
>> number of bits for that matter? I'm not sure, but I have a feeling
>> it saves waveform data, not the actualy wave (like instead of saving
>> a wave like a sample, it saves it as a frequency and volume or
>> sommin.) If that's true, then in theory a decoder could decode at an
>> infinite bit res.
As I understand it, an MP3 encoder performs a Fast Fourier Transform on
the original sample data, which converts the waveform into the 'spectral
domain'. The data now consists of snapshots of frequencies, amplitudes
(and probably phase information) - imagine a video-recording of a hi-fi
specrum analyzer! Then it throws away the data it thinks humans are
least likely to notice until the data fits within the selected bit-rate.
At playback, the player tries to reconstruct the original data through
re-synthesis - generating and overlaying sine waves at the right
frequencies, amplitudes and phases.
No wonder it eats processor time!
(The above explanation probably isn't 100% accurate, but should provide some
insight into why talking about 16-bit isn't totaly relevant for MP3 - the
confusion stems from people saying MP3 is CD-quality - maybe it is, but the
data isn't stored in the same domain, so direct comparisons aren't
appropriate).
All the best,
Windows 95: The Dracula of Operating Systems--it sucks up all your
memory, bleeds your hard drive dry, and only works an average of
12 hours out of every 24.
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