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


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.



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.)



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:-


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.


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

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