From a programmer point of view, upsampling is required when the
ratio among the two sample rates is fractional. In such a case the
original signal must be upsampled to the minimum common multiple of
the two rates, then filtered, then downsampled to the destination ratio.
Here different algorithms, including those that do dithering, may
produce slightly different results.
In many chips that do sample rate conversion (SRC) in real-time, for
example in the digital inputs of many low-cost AD/DA boards,
upsampling filtering and rate conversion are performed regardless of
the input and output sample rates. As every device has its own clock
that could slightly differ from other devices, SRC adapts the sample
rates among two different devices, but could introduce degradation of
the signal, in particular around the Nyquist frequency that is half
of the sample rate.
An accurate digital transfer can be performed only when the digital
input is able to lock on the incoming clock; this is possible when
only 2 devices are connected, e.g. a DAT recorder connected to a
sound board for digitally copying a DAT recording to a PC.
When great accuracy is required in a multiple devices environment,
e.g. a recording studio, a master clock should be distributed to all
digital devices to have all them in synch.
Gianni
At 08.29 15/02/2009, you wrote:
><<"Making the original recording with 88.2 kHz means the
>reduction to 44.1 is simpler (just throw out every other sample) than,
>say, the conversion from 96 kHz to 44.1 kHz."
>This is incorrect. When doing sample rate conversion from 88.2 to
>44.1, the process that sounds best is not a simple subtraction of half
>of the data. The conversion includes dithering and interpolation,
>too, which makes the process very similar to that used to convert from
>96K samples to 44.1K samples.>>
>
>The process involves multiplying first, then dividing. Whether 96k or
>88.1, the file is upsampled to a very high SR rate, then divided down
>to 44.1k.
>
>Scott Fraser
>
>
>
>
>Nessun virus nel messaggio in arrivo.
>Controllato da AVG - www.avg.com
>Versione: 8.0.237 / Database dei virus: 270.10.23/1952 - Data di
>rilascio: 02/13/09 18:29:00
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----------------------------
Gianni Pavan
Centro Interdisciplinare di Bioacustica e Ricerche Ambientali
Universita' degli Studi di Pavia, Via Taramelli 24, 27100 PAVIA, ITALIA
Phone +39-0382-987874 Fax +39-02-700-32921
Email
Web http://www.unipv.it/cibra
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"While a picture is worth a thousand words, a
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause
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