I'm preparing a new opamp board and I intend to make the load resistance switchable. Where can I read more about Hans' findings? I'm not sure what values to include.
I know this is old.... just picked up on it.
"Have you actually measured the response of those low frequency digital filters to verify they perfectly match the roll off frequency and slope you are designing to. Digital filters hit a wall due to limited precision of the 28 bit word and 56 bit accumulator when running 96 kHz sample rate and low frequency filters. Maybe you are running lower sample rate for the low frequency filters or double precision coefficients ( 56 bits ) or something. You can see the effect in simulation as well as in the firmware. "
A few comments:
- I actually run them at 48Ks/s - I am too much the engineer to be convinced there is anything going to sneak through at much higher frequency.
- I do not use the MiniDSP tool suite, this is a custom coded application
Yes, I have measured them as part of testing of the design. I did not specifically measure the rolloff rate, but did not notice anything that struck me as being out of whack.
All coefficients in the processing chain is double as my application was so far short of the capacity of the ADAU device that I had no reason to conserve memory.
"I would like to see miniDSP add a sample rate conversion and run the low frequency filters at a lower sample rate, say 11 ksps, so they would work properly with the limited precision math."
Other than 'Because I can" is there a reason why you are running at even 96Ks/s?
"Have you actually measured the response of those low frequency digital filters to verify they perfectly match the roll off frequency and slope you are designing to. Digital filters hit a wall due to limited precision of the 28 bit word and 56 bit accumulator when running 96 kHz sample rate and low frequency filters. Maybe you are running lower sample rate for the low frequency filters or double precision coefficients ( 56 bits ) or something. You can see the effect in simulation as well as in the firmware. "
A few comments:
- I actually run them at 48Ks/s - I am too much the engineer to be convinced there is anything going to sneak through at much higher frequency.
- I do not use the MiniDSP tool suite, this is a custom coded application
Yes, I have measured them as part of testing of the design. I did not specifically measure the rolloff rate, but did not notice anything that struck me as being out of whack.
All coefficients in the processing chain is double as my application was so far short of the capacity of the ADAU device that I had no reason to conserve memory.
"I would like to see miniDSP add a sample rate conversion and run the low frequency filters at a lower sample rate, say 11 ksps, so they would work properly with the limited precision math."
Other than 'Because I can" is there a reason why you are running at even 96Ks/s?
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