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SigmaStudio sample rate registers

Question asked by GregAB on Sep 30, 2011
Latest reply on Oct 6, 2011 by awalshe

We have the audio codec running but there is a question about the sampling rate that would resolve the issue to our satisfaction. In the Sigma Studio software, there are hardware register settings that set the sampling rate of the chip such as serial port sampling rate, ADC sampling rate and DSP sampling rate. For our application, we set the core clock frequency to 48 KHz and the three sampling rates mentioned to 12 KHz. When testing our system, I set up a square wave source in the schematic window of Sigma Studio to the output and then played it back through our system. There is a field, sample rate window, which can be accessed by right clicking on the square wave source that I set to 12 KHz to match the hardware register settings. When I analyzed the square wave coming over the I2S bus however, the frequency I measured was 750 Hz vs. the 500 Hz the square wave source was set to. The only way to get the frequency I was expecting was to set the sample rate window setting to 18 KHz. This was the case regardless of what frequency I set the square wave source to.

 

My question then is: why must the sample rate window be set to 18 KHz when the hardware registers are set to 12 KHz and the core clock frequency is 48 KHz?

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