I am testing the device with Sine wave tones ranging across the voice band
between 300Hz and 3400Hz and
Am finding that with a sampling rate of 16Khz, I am getting a 25% reduction in
output at 3400 compared
Is this attenuation the correct operation of the device? I was expecting a flat
Are there any setings in the registers which affect the frequency response?
I found that 8Khz sampling gave distortion to the wave at 3400Hz so increased
This is actually the correct or expected frequency response of the device. It
uses a Sinc^3 filter to provide low group delay - however this filter response
is quite "soft" with roll-off in the pass band that continues into the
If the device is being used with a DSP as is normally the case, a Sinc^3
compensation filter operating at 16 kHz with decimation to 8 kHz can provide a
flat response out to 3400 Hz and provides a sharp transition band.
The other alternative is the AD74111 which is a mono codec but has a more
traditional filter which gives flat pass band response and sharp transition