Audio "popping" during stereo playback and Pass-through recording not working

[drp0]

This library is quite an achievement in a limited cpu! I am using a mega. The following pcmConfig.h is in use: #define buffSize 254 #define SD_FULLSPEED #define SDFAT #define STEREO_OR_16BIT #define ENABLE_RECORDING #define BLOCK_COUNT 10000UL

1. During playback of a 2 channel 8bit 16000 Hz wav file the left channel exhibits an audible level of hum/popping noise. This does not appear with mono wav files. Swapping the speakers moves the distortion to the right side. Both channel pins are passed to a small amplifier through 1uF capacitors. Any hardware/software recommendations for aleviating this?

2. I can record wav files with satisfactory results. However I can not get pass-through to work at all. Any recommendations?

David

[TMRh20]

Hmm, I’ll have to try recreating the issues here to give u a good answer I think. Gimme a bit of time…

On Jun 11, 2022, at 4:11 AM, David Patterson @.***> wrote:

 This library is quite an achievement in a limited cpu! I am using a mega. The following pcmConfig.h is in use: #define buffSize 254 #define SD_FULLSPEED #define SDFAT #define STEREO_OR_16BIT #define ENABLE_RECORDING #define BLOCK_COUNT 10000UL

During playback of a 2 channel 8bit 16000 Hz wav file the left channel exhibits an audible level of hum/popping noise. This does not appear with mono wav files. Swapping the speakers moves the distortion to the right side. Both channel pins are passed to a small amplifier through 1uF capacitors. Any hardware/software recommendations for aleviating this?

I can record wav files with satisfactory results. However I can not get pass-through to work at all. Any recommendations?

David

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[TMRh20]

1. You might want to try using different timer pins. Mega supports pin pairs 5-2, 6-7,11-12,45-46. I'm guessing its due to some internal harmonics, so using a different timer may alleviate the issue. I haven't been able to recreate this issue.
2. Pass through wouldn't work for me using pin pairs 5-2 but worked using 11-12. Something odd going on there. I'm not sure of the cause yet, but at least there is a workaround.

[drp0]

I was already working on pins 11 and 12 plus analogue 1. As per your suggestion I tried 5-2 and 6-7. I also tried Analogue 0. Pins 45/46 not tested as they are covered by the sd card. No change in the left channel distortion. No passthrough. Just in case the amp was on the fritz I swapped the wires to 11/12 and the distortion moved to the right. Recording with pass-through is recording. Should passthrough work with stereo enabled? I did try with it off- still no pass-through.

How would you recommend connecting to an amp? I tried 100nF, 1uF and 10 uF series capacitors- no difference to the distortion.

David

[drp0]

I attached a more powerful amplifier. Left channel audio distortion still present. However, passthrough audio is present at very high gain levels. I presume there is no digital signal gain on the pass-through channel? Certainly setVolume seems not to affect it and a quick look at your recording code seems to suggest no amplification.

My microphone amp produces perfectly audible recordings with setVolume(4); for playback.

David

[Sorush-moradisani]

I'm using Arduino mega with PAM8403 amplifier. the volume was fine but had tremendous amount of noise and squeaking. you can completely remove noise and relatively improve sound quality by connecting a 10uf capacitor between output pin and GND (or input of amplifier) .