> * Peter Jaques <[EMAIL PROTECTED]> on Tue, 05 Jun 2001
> | for uncompressed 16 bit stereo pcm, you're essentially
> dealing with a
> | square wave of 16 bits/channel * 2 channels * 44100 Hz = 1411200 Hz.
> | that's extremely high to just spit onto what is
> mechanically no different
> | from a metal cassette.
>
> The highest frequency that 16-bit PCM can achieve is 22.01kHz, and is
> represented by 16 "on" bits plus the frame. Those 16 "on"
> bits take up
> exactly the same ammount of space as one frame of dead
> silence, 16 "off"
> bits. Frequency has no direct relevance to how much space is
> required to
> store the signal, only resolution of the sampling.
I have a been lurking on this list for a while, but I feel that I must
correct something that is just, plain wrong. The value of one sample gives
only amplitude information, and no frequency information. For that you need
multiple samples as it is the differences between samples that contains the
frequency information. If each sample is treated as signed number, the
sequence of samples ..., +n, -n, +n, -n, ... represents a sine wave at half
the sample frequency, i.e. 22.01kHz for a 44.1kHz sample rate. The value of
n determines the amplitude, i.e. volume, of the sound.
Secondly, the frequency DOES have a very definite relevance to the space
required to store the signal, though, as the original poster was saying, it
is the sample frequency that matters, not the signal frequency. Having said
that, the bandwidth required to store the signal is actually determined by
the symbol rate, and not the bit rate, per se. So, 1.4Mb/s could be stored
with 0.7Mhz bandwidth if two bits were stored per symbol. The problem with
the calculation in the original post was that you can't store the raw data
without some kind of error correction because digital distortion - i.e. bit
errors - sounds BAAAD, and this adds an overhead. However, although the
bandwidth required is much higher than analogue sources - even when
compression is used, the signal-to-noise ratio of CD/MD (caused by
quantisation noise) is so high that the limit is usually in the analogue
stages used to reproduce it. The wow, flutter, hiss, popping, cracks, etc.
of the various analogue systems is often easily perceptible on even modest
systems.
OK, I'll get off my high horse now,
Steve.
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