Go Down

Topic: SimpleSDAudio "hiss" static sound (Read 612 times) previous topic - next topic

Jabbadabbadahaht

Sep 13, 2016, 04:45 pm Last Edit: Sep 13, 2016, 05:00 pm by Jabbadabbadahaht
Hello i have hudge problem with my project. I want to build a clock with 7digit display that will play some sounds if triggered i used  SimpleSDAudio libfor that + simple 5v amp. But when it starts playing sound it has rly annoying static - and i dont know how to  get rid of it.


https://drive.google.com/open?id=0B94O7YSioJN7MmV2U1NadG50azg

DVDdoug

I haven't used that library, but probably  because it's 8-bits and because it's PWM.     An audio shield with a real PCM DAC and 16-bits should work a lot better.

With 8-bit audio you can hear the quantization noise.    Quantization noise is most noticeable with quiet sounds.    But, there is no quantization noise with dead-digital silence, and "digitally-loud" sounds (using all 8-bit of amplitude) can largely mask the noise.   (Analog amplification won't help because it amplifies the signal and noise together, making the noise even more noticeable.)

 

Grumpy_Mike

That noise sounds like it is being generated in the amplifier by having a high frequency PWM signal applied to it. How loud is this noise when you are playing a sample? Here is an example of direct connection of PWM to an amplifier playing a sample:-

https://vimeo.com/178616334

I find that this noise is worst on some amplifiers than others.

One way to reduce it is to have a reconstruction filter on the output. This is a low pass filter with a roll off frequency at the sample rate. The PWM rate should be many times higher than the sample rate. Also AC couple into your amplifier with at least a 4u7F capacitor.

Jabbadabbadahaht

Well sound is almost same level as playback. Im going to try 4u7F capacitor.

Go Up