MiniDSP interpolation question

Hi Bing,

This is because the interpolation multiplier changes the modulator rate. The modulator likes to operate at a certain frequency, and if you lower the multiplier, without increasing the sampling rate, then you are changing the modulator frequency. To use the 4X interpolator, you will want the sampling rate around 88.2 kHz or 96 kHz, for 2X you will want it near 176.4 kHz or 192 kHz.

Justin

Hi Justin,

Thanks a lot,

About 48K and 96K ,I used 8X sampling rate,about 192K ,I used 2X, THD curve looks well ,but from your explain and our datasheet,It seems that 96K sampling rate can not support 8X?

Hi Bing,

When using a 96 kHz sampling rate, the interpolation should be at 4X.

Justin

Hi Justin,

1. Could you explain what  is the certain frequency of the modulator and why it is a certain value? Is it the OSRCK?

if fs=48K ,16fs=768K. if fs=192K ,16fs=3.072M, It sees not the certain value.

I have tested the frequency spectrum of using 4X and 2X at 48Khz Sampling rate ,a lot of spur comes out (Input signal frequency is 16K),but I don't know the root cause of this issue.

Hi Bing,

When operating in multiples of 48 kHz, the modulator is designed to run at 6.144 MHz. This means that if you try to change the rate of the modulator, by using the 2X or 4X when a 48 kHz sampling rate is use, the modulator will not perform as specified in the data sheet. This is the cause of the noise you are seeing.

Justin

Hi Justin,

How about modulator frequency of 96K /192K sampling rate, is it the same with 48K,6.144M?

The formular is K*fs=6144K/16=384K, so if fs=48K,K=8,right?

Hi Bing,

Yes this is correct. For 44.1 kHz multiples the modulator clock will be 5.644 MHz.

Justin