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Subject: RE: Frequency as it relates to recording quality
From: Michael O'Quinn (michael_at_oquinn.info)
Date: 2003-04-10


Hi David,

Generally, 44.1 is used with music MP3's, and the encoding bitrate is
adjusted based on the quality -vs- size balance. In my experience lower
sampling frequencies are primarily used when the audio is NOT compressed,
such as with a *.wav file, or with non-music applications.

One of the reasons that 44.1 kHz sampling frequency is so popular is
that it's what regular audio CD's use.

The direct answer to your questions is "Yes -- that's why they exist."

I think you are asking if YOU would ever need to use them, and my response
is that if you are just ripping CD and encoding MP3, stick with 44.1
sampling and set the bitrate as you see fit. I can't answer about
recording voice with the Archos -- any ABJR owners care to chime in with
some practical advice?

Other than that, the fact that you have to ask the question says (to me,
at least) that you likely will not need to go there, unless you are wildly
curious (a common trait among subscribers to this list) in which case you
need to go find some good material and read up on it.

If you ARE curious, one good web-site I've found is...

   www.r3mix.net

This site is not so much about the theory of sampling frequencies, but
it's good on the actual results of different ways of encoding MP3s. There
are other places to look, of course.

I hope this helps!

Michael

On Wed, 9 Apr 2003, David Reis wrote:

> Thanks much for the wealth of info.
>
> I would imagine from this that "most" recording of live music disregarding
> disk space requirements should be done @ 44.1
>
> Are there times when a higher (48) would be used?
>
> Are there times when a lower (16) would be used?
>
> Any thing less than 44.1 used simply to save disk space?
>
>
> Thanks again
> Bubba
>
> -----Original Message-----
> From: ajf [mailto:ajf_at_midmaine.com]
> Sent: Wednesday, April 09, 2003 3:38 PM
> To: rockbox_at_cool.haxx.se
> Subject: Re: Frequency as it relates to recording quality
>
>
> The sampling frequency is the number of times per second an audio is
> sampled. CD audio is sampled at 44.1 KHz, which means 44,100 samples per
> second. CD audio uses 16 bit samples, so the size of an uncompressed CD
> audio file is 44,100 x 16 bits per second x 2 (stereo) or about 10 MB per
> minute.
>
> According to Shannon's Law, we can hear sounds at a frequency up to 1/2 the
> sampling rate, which makes 44.1 a good choice, because the range of human
> hearing tops out under 20,000 Hz and declines as we get older. If you were
> recording human speech, you might use 22.05 KHz sampling, because the
> highest frequencies usually encountered are around 8 KHz. That would halve
> the size of the file.
>
> The "bitrate" refers to the degree that the file is compressed. The lower
> the bitrate, the more the file has been compressed and sound quality is
> lost, but the smaller the file. A 128 kbps mp3 will run about 1 MB per
> minute (128 x1024 x60 / 8 bits/byte) , a 10-fold reduction, but the sound
> difference from the original will be apparent.
>
> Most experts agree that at bitrates above 192 kbps, any loss of quality is
> hard to detect, but at that bitrate, the file will be 50% bigger.
>
> It is a trade-off of size vs quality.
>
>
> David Reis writes:
>
> >
> > Can anyone give me some quick details on how the frequency affects the
> > recording quality.
> >
> >
> > Thanks,
> > Bubba
> >
> >
> >
> >
> >
>
>
>
>



Page was last modified "Jan 10 2012" The Rockbox Crew
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