Re: podcasts?

Sean wrote: 
On 7/12/05 4:15 AM, "Curt Fischer"  typed:


someone wrote:


That is correct too, but can you show me the difference between a 196
kbps MP3 and the original ? Because frankly I don't hear it, so I don't
care at all.


I'm not sure what sampling rate the usual mp3 is at, but in a
side-by-side comparison IME it is easy to tell the mp3 from the
uncompressed source by listening to high end sounds like e.g. the
cymbals or snare.  I can't say that I get hung up on this issue or even
notice it outside the context of a side-by-side comparison though.

For language learning its probably not that important, at least for
Japanese.



The usual MP3 has a sample rate of 44.1 khz. This is exactly the same as red
book standard CD audio. Audio sampled at 44.1 khz reproduces frequencies up
to 22.05 khz (that's half of the sample rate, in case you didn't notice).
Human beings generally can't hear frequencies above that, although some
folks say even the unheard higher frequencies have some effect on the
quality (tone, colour) of the sound.
MP3 compression involves a much more complicated process than simple hacking
away at the waveform. When you say you can perceive the difference between
CD audio and MP3 by some difference in the high-end, I'd say you might be
misinterpreting the difference you hear.

Have you ever tried a side-by-side comparison? The difference is noticeable, although perhaps not with a 196 kbps mp3, which is what the guy was talking before my top quoted response above.

My understanding of the mp3 encoding process is not detailed, but I thought that more or less, Fourier transforms of the source are taken as functions of time (which involves inevitable frequency cutoff due to the finite time domain over which the FT is taken). Next, peaks in the frequency domain for a given time point are "sharpened" by removing lower-intensity frequencies present around the peak frequency. This works because of some sort of masking phenomenon with human hearing that says that if you have a say 50 dB sound at 440 Hz then no one can hear a 30dB sound at 441 Hz. This sharpening provides most of the compression, right, but is obviously a lossy process, right?

--
Curt Fischer
.

Relevant Pages

  • Re: podcasts?
    ... noticeable, although perhaps not with a 196 kbps mp3, which is what the guy was talking before my top quoted response above. ... My understanding of the mp3 encoding process is not detailed, ... 30dB sound at 441 Hz. ... way the compression works: elements of the Fourier ...
    (sci.lang.japan)
  • Re: One more little question
    ... > How does one change the key of a mp3 or wave file. ... Changing the key is done by multiplying all the tone frequencies present ... between the two with Fourier's transform. ... the problem is that the encoded data need to be uncompressed first. ...
    (alt.comp.lang.borland-delphi)
  • Re: podcasts?
    ... >>> My understanding of the mp3 encoding process is not detailed, ... >>> 30dB sound at 441 Hz. ... > way the compression works: elements of the Fourier ... the simple hacking off of higher frequencies and lower frequencies ...
    (sci.lang.japan)
  • Re: Nyquist, quantization and windowing gotchas
    ... at 22 kHz and saved as mp3). ... One possible place for error is when the original contains frequencies ... smaller heads. ...
    (comp.dsp)
  • Re: podcasts?
    ... side-by-side comparison IME it is easy to tell the mp3 from the uncompressed source by listening to high end sounds like e.g. the cymbals or snare. ... Human beings generally can't hear frequencies above that, ... Depending on the bitrate this filtering can be rather drastic. ... bitrate: 112kbps -> cutoff freq.: 15,8kHz bitrate: 128kbps -> cutoff freq.: 17,2kHz bitrate: 160kbps -> cutoff freq.: 17,9kHz bitrate: 192kbps -> cutoff freq.: 19,3kHz ...
    (sci.lang.japan)
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