HI, this is my first DSP project (a three-way audio crossover, with speaker compensation).
I already have a Sure ADAU1701 board, with relevant programmer.
I would like to add a SPDIF input, with multi-rate capability (from 44.1 to192KHz), but I haven’t found any suitable (and reasonably priced) ready-to-use ASRC board and I have not the skill (and the patience) to design one.
So, I am considering to use the analog equivalent of ASRC, that is:
SPIDIF source > SPDIF receiver/DAC > analog filter > ADAU ADC.
(I already have several SPDIF receiver/DAC).
The critical part of this solution is clearly the analog filter, needed to avoid aliasing of the ADAU ADC; I don’t know how to dimension this filter (I don’t know the oversampling ratio of the ADAU ADC), but I think that a 8th order low pass filter based on a LTC1064-x ic will be adequate (elliptic LTC1064-04 has 80dB Stopband Attenuation at 2 x fCUTOFF).
In order to make this filter work at a fCUTOFF of about 20KHz, I need a clock of about 1MHz or 2 MHz (depending on the LT1064 setting).
The question is: is it possible to derive this clock directly from a GPIO of the ADAU1701 and, more general, is this solution feasible?
Note that this filter will be useful also when, for example, the analog output from a CD player is connected to the ADAU ADC (in this case the aliasing could be produced by the images present in the output spectrum of the DAC inside the CD player).