Leif Asbrink wrote:
My concern is non-integer rate conversion. A soundcard
that actually samples at 3.072 MHz and sends 48 kHz to
the PC has to be down-sampled by 1.088435 times to
produce 44.1 kHz. If it were properly done in the PC it
would be perfectly OK, but judging from my experiment,
the Windows device driver is not very accurate.
My problem: How come that the computers do not ask
"do you really want a rate conversion ?" when the user
sets a speed that will cause a non-integer conversion?
In Windows you can choose the compromise between quality of the resampling and
resources utilized for that.
Click on Control Panel | Sound and Audio Devices | Audio | Advanced | Performance and in the bottom part of the panel
you are now in, you will find a slider labeled "Sample rate conversion quality". It is advisable to keep it at its
extreme right, the best quality.
Anyway in Winrad I coded a non-integer resampling routine using the method of interpolation on a windowed sinc. The
results seems to be quite good, the spurs generated by the resampling are usually between -90 and -100 dBc (if I recall
correctly). I wonder which algorithm does use Windows. The interpolation is quite fast, the CPU used is minimal.
73 Alberto I2PHD
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