Here are the measurements of my dspMusik RIAA EQ and SP-9 both actual and error from theoretical. Gains were normalized to 0.0 dB at 1 KHz.Magnitude and Phase ResponseMagnitude and Phase ErrordspMusik:
- The low frequency phase error is most likely due to AC coupling on the input of the dspMusik (Rich - can you confirm?), but I believe that to be very negligible.
- The high frequency error is due to warpage of the digital filters (96 KHz Nyquist). In the critical range, the error is within ~0.16 dB
- NO external circuitry was in the measurement loop - this is from dspMusik Analog Input to its DAC Output (I routed the RIAA EQ filters directly to a DAC output)
- The low frequency phase error is most likely due to AC coupling on the input
- The high frequency error is very minimal due to all analog circuitry.
I think the dspMusik RIAA is quite competitive in response in the critical audio range. Listening will tell if the HF response error in the dspMusik is audible (to me) or not. I'm nearly 65, and my hearing most likely will never detect the response errors above 20 KHz.Some notes:
I calculated the theoretical transfer function response using the 3180 uS, 318 us, and 75 uS time constants used in the RIAA reference response.
Measurements were made with a Keysight EDUX1002G digital oscilloscope using its built-in function generator and transfer function analysis software. Resolution was 50 pts/decade in a log sweep. Data was transferred to the spreadsheet for plotting the graphs shown above.[/list]