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Noise from the low bits with BF526 and SSM2603

Question asked by dav on Sep 19, 2011
Latest reply on Oct 7, 2011 by Prashant

Hi,

 

We get noise listening to the analog output from the ssm2603 when sending a signal with a low amplitude from the Blackfin on a rev 1.1 ADZS-BF526-EZBRD. The noise sounds like a tone or filter sweep and seems to be directly related to the absolute amplitude of the signal.

 

Attached is a slightly modified version of Analog's 'loopback' project.

For a sound-demo of the issue, check the demo video attached.

 

The source is modified to output either a square or a sine, controlled by this define

//#define SQUAREWAVE

#define SINEWAVE

 

The signal is lowered in volume either in discrete steps by shifting it down or scaling with a multiplier. Select method with:

//#define BIT_SHIFTS

#define MULTIPLIER

 

Otherways I'm using all the default settings from Analogs loopback example, except for SSM2603_WLEN_32 for 32 bit word length.

 

 

Note as the signal will be quite low in volume from the EZ-board needs to be powered from the battery and the programmer should be disconnected.

 

Has anybody else experienced this noise? Have I made some obvious mistake?

My gut feel is that there is some mismatch in the setup of the I2S communication.

 

Any input greatly appreciated.

/Dav

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