Hello.
I have searched this forum and Google for solutions for my issue, but couldn't find any (yet).
I'm trying to make a minimal record (voice) and play device using Teensy 3.1, ADC input circuit (in Teensy Audio library github), microphone with a simple npn transistor amplifier, and DAC output with an earphone. No audio shield or any other fancy stuff.
I tried direct connection (ADC1 to DAC1) without recording and the sound quality was fine, negligible noise. But with the recording set up (ADC to Queue and playSdRaw to DAC), there is constant loud noise. The noise is very similar to the one in this post.
I also tried to disconnect A2 (ADC) and record expecting just low level white noise since there is no mic-amp input, but the noise was still there.
The power source was lipo battery and I tried bunch of different size of electrolytic capacitors to the AGND and VCC, but didn't help.
Playing WAV file from the SD card was also fine. Actually the sound quality with this minimal configuration was quite impressive. So, I don't really think this is some sort of ground loop or decoupling issue. If it is, the noise should be there when I play the WAV file as well. Please correct me if I'm wrong.
Any suggestions and advice would be greatly appreciated.
Jinseok
I have searched this forum and Google for solutions for my issue, but couldn't find any (yet).
I'm trying to make a minimal record (voice) and play device using Teensy 3.1, ADC input circuit (in Teensy Audio library github), microphone with a simple npn transistor amplifier, and DAC output with an earphone. No audio shield or any other fancy stuff.
I tried direct connection (ADC1 to DAC1) without recording and the sound quality was fine, negligible noise. But with the recording set up (ADC to Queue and playSdRaw to DAC), there is constant loud noise. The noise is very similar to the one in this post.
I also tried to disconnect A2 (ADC) and record expecting just low level white noise since there is no mic-amp input, but the noise was still there.
The power source was lipo battery and I tried bunch of different size of electrolytic capacitors to the AGND and VCC, but didn't help.
Playing WAV file from the SD card was also fine. Actually the sound quality with this minimal configuration was quite impressive. So, I don't really think this is some sort of ground loop or decoupling issue. If it is, the noise should be there when I play the WAV file as well. Please correct me if I'm wrong.
Any suggestions and advice would be greatly appreciated.
Jinseok