Help with all this digital stuff?

[deadearnest]

How I wish I knew what all this meant!!!!!!!!
Andy G.
----- Original Message -----
From: Paul Mather <paul at GROMIT.DLIB.VT.EDU>
To: <BOC-L at LISTSERV.ISPNETINC.NET>
Sent: Wednesday, May 12, 2004 3:23 PM
Subject: Re: Help with all this digital stuff?


> On Thu, May 06, 2004 at 05:07:45PM +0100, M Holmes wrote:
>
> => OK, that makes sense. So what bitrate would give CD quality? The lowest
> => bitrate for MP3 seems to knock nearly 90% off the filesize. Presumably
> => that means the quality is quite poor? What do others use as the
> => reasonable compromise on portable players?
>
> Actually, the lowest bitrate for MPEG audio would knock more than 90%
> off the filesize.  Normal linear PCM audio (as on a CD) consists of
> 16-bit stereo samples at a sample rate of 44.1 KHz.  So, that's a
> bitrate of 44100*16*2 = 1411200 bps of data.  Here are the supported
> bitrates for MPEG layer 3 audio:
>
> MPEG-1   layer III sample frequencies (kHz):  32  48  44.1
> bitrates (kbps): 32 40 48 56 64 80 96 112 128 160 192 224 256 320
>
> MPEG-2   layer III sample frequencies (kHz):  16  24  22.05
> bitrates (kbps):  8 16 24 32 40 48 56 64 80 96 112 128 144 160
>
> MPEG-2.5 layer III sample frequencies (kHz):   8  12  11.025
> bitrates (kbps):  8 16 24 32 40 48 56 64 80 96 112 128 144 160
>
>
> So, for 44.1 KHz audio, the lowest bitrate is actually 32 kbps.  That
> amounts to more than a 97% saving over the original audio stream
> size.  If you were also prepared to downsample (say to 22.05 KHz), you
> could use an 8 kbps bitrate (MPEG-2 layer 3) for a greater than 99%
> reduction in size compared to the original uncompressed audio.
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