Weird inverted output from codec....(with pics)

wildswan · 30th July 2010, 03:18 PM

Hi all,
I'm using an ARM microcontroller to interface with a PCM3060 24 bit codec using I2S.

I am trying to generate a sine wave using a lookup table.

Trouble is that the top and bottom halves of the sine wave are flipped over!!

Anyone got any ideas?

wildswan · 30th July 2010, 04:04 PM

Ok problem solved. I was using positive values only with what I thought was an unsigned int. The library for the micro indicated an unsigned 16 bit int, so I used values from 0-65535 for the sine.

When I plugged both positive and negative values (-32768 to 32768) for the look up table the problem went away.... strange but there ya go. Variable must have been maxing out and resetting to 0 etc...

Hope this helps someone else sometime :-)

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30th July 2010, 04:04 PM	#2
wildswan diyAudio Member Join Date: May 2006	Ok problem solved. I was using positive values only with what I thought was an unsigned int. The library for the micro indicated an unsigned 16 bit int, so I used values from 0-65535 for the sine. When I plugged both positive and negative values (-32768 to 32768) for the look up table the problem went away.... strange but there ya go. Variable must have been maxing out and resetting to 0 etc... Hope this helps someone else sometime :-)