Line-in loop-back code producing distortion

Codie Wilson

I am using the C5505 ezdsp usb stick. Any time I use line-in loop-back code for audio (such as from an ipod), I get a clean-sounding signal out. When I use a function generator to loop a pure sinusoid (for example, 1kHz sine wave), the output as seen on an oscilloscope is an extremely noisy sine wave. I've used multiple generators, oscilloscopes and cables to make sure that wasn't the issue. I connected the output to a spectrum analyzer to see if I could find extra spectral components which would be causing the noise, but I couldn't find anything. I suspect the noise might be at frequencies that are beyond the audible range, and therefore I can't hear them. Has anyone else had this problem?

Thanks.

over 14 years ago

0 Codie Wilson over 14 years ago

Prodigy 40 points

I can also generate a much cleaner sine wave just using the tone generator example code. Not sure what the problem is with loop-back code.

0 Mark M over 14 years ago in reply to Codie Wilson

TI__Mastermind 30110 points

Hi Codie,

This is interesting.

Can you attach your project? Is the signal generator sharing a common ground with the eZdsp (ie. eZdsp plugged into USB on PC and PC is plugged into same outlet as signal generator).

Thanks,
Mark

0 Codie Wilson over 14 years ago in reply to Mark M

Prodigy 40 points

Actually, it's not even project code. It's happened with test code that comes with the usb stick, and also the ezDSP audio filter demo project downloadable online at http://code.google.com/p/c5505-ezdsp/. However, sine wave generation straight from the board using demo code works much better. Listening to audio also does not produce any noticeable problems in sound quality.

Thanks,

Codie

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Line-in loop-back code producing distortion