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I2S - Digital Audio

Tue 26 July 2016


Setting up I2S audio isn't too hard. I used a Adafruit i2s 3W amp (MAX98357A), to hook it up to my rpi3. Also the i2s-mmap seems to help with any popping noise.

Edit /boot/config.txt:

# dtparam=audio=off

Create/edit /etc/asound.conf to setup default audio:

pcm.hifiberry {
  type hw card 0

pcm.!default {
  type plug
  slave.pcm "dmixer"

pcm.dmixer {
  type dmix
  ipc_key 1024
  slave {
    pcm "hifiberry"
    channels 2

ctl.dmixer {
  type hw
  card 0

Now you have to reboot so the system gets setup correctly (remember, these are boot parameter settings).

Now connect the amp to the rpi where Vin is 5V:

DIN 21 40
BCLK 18 12
LRCLK 19 35

Now, lots of instructions on the internet say to disable i2c, but you don't have too. The bottom part of my /boot/config.txt looks like this:

# Enable audio (loads snd_bcm2835)

As you can see, I leave i2c on. Note the enable_uart=0 is so I can use bluetooth. Apparently, the BT module is tied to the hardware serial port and the don't bother to tell people. You have to spend a lot of time to dig it up.

Jack Server

Not sure you need this:

sudo apt-get --no-install-recommends install jackd2
jackd -d alsa

I don't seem to use it.


I still had lots of issues. installing sudo apt-get install speech-dispatcher seemed to help. I now had pulse audio and alsamixer working.

If you get errors about unknown cards:

ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2239:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side

Edit /usr/share/alsa/alsa.conf and change the cards from pcm.front cards.pcm.front to pcm.front cards.pcm.default.


Sox has some useful tools:

sudo apt-get install sox libsox2

Other useful ones might be: libsox-fmt-all and libsox-dev.

You can list the devices ALSA see with:

pi@robot ~ $ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: sndrpihifiberry [snd_rpi_hifiberry_dac], device 0: HifiBerry DAC HiFi pcm5102a-hifi-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0

So we see our I2S amp (snd_rpi_hifiberry_dac) listed there, so we are ready to test it:

  1. Random static: speaker-test -c2

  2. Wave file: speaker-test -c2 --test=wav -w /usr/share/sounds/alsa/Front_Center.wav

  3. Tone: play -n synth sin 1000 gain 1

  4. Audio test:

    wget https://cdn.shopify.com/s/files/1/0062/6682/files/sample.wav
    aplay sample.wav
  5. Text to speach:

    sudo apt-get install espeak
    espeak "hello world"
    espeak “Hello World!” > /dev/null

Check File Types

Also, you can see what the file is:

pi@r2d2 tmp $ file sample.wav
sample.wav: RIFF (little-endian) data, WAVE audio, Microsoft PCM, 8 bit, mono 11025 Hz

Or use sox:

pi@r2d2 tmp $ soxi sample.wav

Input File     : 'sample.wav'
Channels       : 1
Sample Rate    : 11025
Precision      : 8-bit
Duration       : 00:00:04.06 = 44800 samples ~ 304.762 CDDA sectors
File Size      : 44.8k
Bit Rate       : 88.3k
Sample Encoding: 8-bit Unsigned Integer PCM

Alsa Mixer

To see what you have access to:

pi@r2d2 ~ $ amixer
Simple mixer control 'Master',0
  Capabilities: pvolume pswitch pswitch-joined
  Playback channels: Front Left - Front Right
  Limits: Playback 0 - 65536
  Front Left: Playback 39344 [60%] [on]
  Front Right: Playback 39344 [60%] [on]
Simple mixer control 'Capture',0
  Capabilities: cvolume cswitch cswitch-joined
  Capture channels: Front Left - Front Right
  Limits: Capture 0 - 65536
  Front Left: Capture 65536 [100%] [on]
  Front Right: Capture 65536 [100%] [on]

pi@r2d2 ~ $ amixer controls
numid=4,iface=MIXER,name='Master Playback Switch'
numid=3,iface=MIXER,name='Master Playback Volume'
numid=2,iface=MIXER,name='Capture Switch'
numid=1,iface=MIXER,name='Capture Volume'

Now to make some changes:

  • Get the current value: amixer cget numid=3
  • Set the current value: amixer cset numid=3 50%
  • Mute all sound (switch Master): amixer cset numid=4 off
  • Save changes to /var/lib/alsa/asound.state: sudo alsactl store
  • Reset system if you f@$k up: sudo /etc/init.d/alsa-utils reset

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