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Miniamp + Pi Zero + Csound = distortion?

Scott March Smith

January 06, 2021 03:58

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Hello all,

I've got a set of MiniAmps running on Raspberry Pi Zero WH boards, working towards a multichannel sound installation. I am consistently experiencing distortion with speakers rated for 3W or more, and I'm not sure what the issue is.

I have 5 Miniamps and 5 different Pi Zeros, and the performance is the same across all the units, so I don't think it's defective hardware. I am running a 2 channel csound score on each Pi, outputting a single sine wave with variable amplitude to each channel. I'm running csound at 44100 hz. I am using alsa.

Speakers I've tried:

CUI Devices CSS-66668N

CUI Devices GF1004

CUI Devices GF0668

The only time I've been able to avoid peaking is when I did one of these things:

1: turned the gain down so low in alsamixer that the sound was inaudible from more than a couple of feet from the speaker

2: plugged in a pair of passive Bose speakers, 8 ohm, rated for 10-120W. This sounds GREAT.

3: swapped out the miniamp for an Adafruit I2S Audio Bonnet and plugged in my headphones

I'm kinda at a loss. The only conclusions I can draw: either CUI makes garbage speakers and I should learn my lesson, or that I need speakers with a lot more headroom over the purported 3W output of each miniamp channel. Would love any ideas anyone has! I love the efficiency of the miniamp, and would love to be able to make it work.

Thanks,

Scott

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7 comments

• 0
  
  HiFiBerry team January 06, 2021 07:13

  Did you reduce the output volume? The distortions might be caused by just running a signal at maximum output level.

   

• 0
  
  Scott March Smith January 06, 2021 14:38

  I did -- using alsamixer. I also turned down the output volume of csound. With each of the speakers (except the 120W ones), I had to bring the volume down to almost inaudible levels in order to get rid of the distortion.

  Is there another method I should use for volume control?

• 0
  
  HiFiBerry team January 06, 2021 14:40

  There is no alsamixer control on the MiniAmp. What exactly did you use in alsamixer?

• 0
  
  Scott March Smith January 06, 2021 15:36

  I set up alsamixer to control the volume output by piecing together the configuration from info I found for other amps / DACs, including the Adafruit I2S Audio Bonnet. Totally open to the possibility that I did this wrong! But, it does seem to control the output volume when using the MiniAmp.

   

  /etc/asound.conf

  pcm.hifiberry {
  type softvol
  slave.pcm "plughw:0"
  control.name "Master"
  control.card 0
  }
  
  pcm.!default {
  type plug
  slave.pcm "hifiberry"
  }

   

  In /boot/config.txt:

  
  # Enable HiFiBerry DAC as audio output
  dtoverlay=hifiberry-dac
  dtoverlay=i2s-mmap
  
  [pi4]
  # Enable DRM VC4 V3D driver on top of the dispmanx display stack
  dtoverlay=vc4-fkms-v3d
  max_framebuffers=2
  
  [all]
  #dtoverlay=vc4-fkms-v3d
  gpu_mem=64

• 0
  
  HiFiBerry team January 07, 2021 13:43

  Ok, understood. Unfortunately I can't help at all with csound. Do you see the same problem just playing back an MP3 file with mplayer?

• 0
  
  Scott March Smith January 09, 2021 19:57

  I bounced a wav and mp3 file from csound on my PC, and brought that over to the Pi. It has the same distortion issue as the csound real-time playback.

  However, playing back a couple of mp3s made by other people seems to be fine.. no distortion. :(

  What's weird is that the bounce I made from csound does not peak when playing back on my PC. Is there any reason a file would clip / distort on the miniAmp, and not on an ordinary DAC or sound card?

  Edited by Scott March Smith January 09, 2021 19:58
• 0
  
  HiFiBerry team January 10, 2021 06:49

  I can't say anything about csound, but the fact that "normal" MP3s work, seem to point to csound as the source of the problem. Unfortunately I can't say what might causing this.