Crossovers using high sample rate
We are using an ADAU1450 in a dedicated DAC board with 24/192 data inputs and outputs. We have found that implementing filters below 40Hz for EQ or LF rolloff is not reliable even using 2nd order double precision filters. We experience random LF noises from the DSP under certain circumstances that point to instability in the internal mathematical operations. We tried to do integer downsampling from 192K to 48K for the LF filters then upsample back to 192K to output to the DAC but this did not solve the issues. The only reliable solution that we found was to go to 24/48 input and output data on the ADAU1450 and to perform all operations with double precision at the lower sample rate.
Questions:
1) Why would the integer down/upsampling not work to solve the issue with the LF filters running at 192K?
2) Would it be expected that running filters below 40Hz with a 192K rate even with double precision maths that there could be unexpected mathematical errors?
hardware
processors and dsp
adau1450
SigmaDSP Audio Processors
Processors and Microcontrollers
Hello jstronz,
You did a lot of good testing and gave me some good information.
1) Running the program at 48kHz fs all is good. This is vitally important. This means the filter operates fine at 48kHz fs.
2) Running the program at 192kHz and downsampling the audio to the filter and downsampling the audio and running the filter at 48kHz still has the problem!! This means that the filter is not the problem.
3) What is different between the first point I made and the second point I made is that the serial data coming into and out of the DSP will be different. The sampling rate clock is faster but more important is that the bit clock is a lot faster!! You did not mention the serial audio format you are using? TDM-2? (I2S), TDM-4?
I suspect this issue is with signal integrity of the audio transmission at the higher rate. Either going into the DSP or going out of the DSP. I have no idea how you are connecting to this board?
I think you are getting bit errors.
Unrelated to your issue:
Also, using the ADAU1450 is tough when running at 192kHz fs due to the number of instructions available. The core rate is slower than the 1451 and 1452. SigmaStudio would warn you if you ran out of instructions for one sample period. But, it will limit the amount of processing you can do. This may not be an issue for your application so saving costs by using the 1450 is good!
Dave T
Please log in to reply.