On 2015-07-13 10:14:54 +0100, Jim Lesurf said:

In article , Don Pearce
wrote:
Downsampling from 88kHz is no easier than from 96kHz. You have to go
through the same process of interpolation, upsampling, lowpass
filtering, and finally decimation. Never try to do it by skipping
alternate samples - that way lies alias distortion from quantization.

I'm a bit pun surprised that you wrote that. Makes you look like a
mathematician/theoretician rather than an injuneer. 8-]

The actual real computation of a good 96k - 44.1k conversion does tend to
be far more demanding in terms of number of operations / coefficients / etc
than 88.2 - 44.1k. And I'm not talking about simply discarding, but about
getting at least the same level of quality.

So in theory all you have to do is invoke something like a windowed sinc
convolution and write a nice equation or two on a whiteboard. That works
fine for both. The mathematician can then put the pen down and walk away.
But when it comes to the real number crunching the two cases are very
different for similar quality.

e.g. in a TDA method, a power of two ratio downsample means you only need
one set of coefficients and the clocking is trivial along the arrays. Doing
96 - 44.1 requires rather more effort / complexity for the same output
quality even if you throw the same impulse function at them both. This may
matter both in terms of ensuring you've bugfixed and in terms of CPU
loading or the number of devices on the silicon and the power demand.


And of course every audio ADC uses a massively high sampling rate,
followed by the procedure above to arrive even at 44.1kHz sampling.

Erm, we weren't really talking about the ADC but digital-digital
conversions, probably by running software on a general computing system.
But that doesn't change the above point. And TBH even in hardware like an
ADC or DAC running at a high internal rate, simple integer rations make
good results easier to obtain with less number-bashing.

And of course high rate low-bit tends to risk problems like the ones which
can show up in the 'Health Checks' I did a while ago.

Jim

Any program recommendations for converting 96k/24 to 44k1/16 - non real time?
Ideally linux or mac - or any, if command line.

Arthur

--
Arthur Quinn
real-email arthur at bellacat dot com