On Tuesday, February 15, 2011 2:08:05 PM UTC-5, okeybomb wrote:
> My system`s main function is to sample audio datas,process,and play them
> back.The process core is a ST semi `s STM32F103RC processor,plus TI`s
> TLV320AIC23B audio codec.Of course audio preamps(op amp).The power supply
> is a LM2576.Now the problem is,it is hard to handle the hole noise level of
> this system.Even no process(the signl is digitaly bypass inside the
> STM32),it still has a noise level about 1mVrms.The noise is just like white
> noise,especially low frequncy band.The same situation has also been found
> in another system based on a TI`s TMS320C6720 DSP(they have the same
> function).Could you give me some idea to solve this problem? Buy the
> way,both of the two system has a small level of noise tone sounds like a
> 1Khz.Thank you very much.

You need to know the source of the noise before you can intelligently deal with it. To determine if the noise originates in the codec or before it, short circuit the codec's input and check for noise again. If that is clean, move the short to the input of the pre-amp. 

Jerry
-- 
Engineering is the art of making what you want from things you can get.

My system`s main function is to sample audio datas,process,and play them
back.The process core is a ST semi `s STM32F103RC processor,plus TI`s
TLV320AIC23B audio codec.Of course audio preamps(op amp).The power supply
is a LM2576.Now the problem is,it is hard to handle the hole noise level of
this system.Even no process(the signl is digitaly bypass inside the
STM32),it still has a noise level about 1mVrms.The noise is just like white
noise,especially low frequncy band.The same situation has also been found
in another system based on a TI`s TMS320C6720 DSP(they have the same
function).Could you give me some idea to solve this problem? Buy the
way,both of the two system has a small level of noise tone sounds like a
1Khz.Thank you very much.