[arm-allstar] ARM-allstar Digest, Vol 82, Issue 22

[cqdogxray at gmail.com]

>> I remember, some time ago, you mentioned that simpleusb has filters to
prevent anti-aliasing. Does this only apply to TX audio?

The data on the receive side cannot include any audio components above 4
kHz, so no similar anti-alias filters are needed.  The USB fob D/A converter
is driven at 48 kHz, so the filtering you need is up at that frequency range
and hardware-based (after the D/A converter).

On the transmit side I find it helpful to limit the energy starting at 3 kHz
because there are  just not very many bits/sec available for digitizing that
energy in that range and the result is in increasing distortion products
(not including aliasing).   

This is at odds with audio from YSF whose vocoder does some magic to pump
through a lot of energy in that audio frequency range .... (vocoder vs
codec).

Ken/KE2N