Issues accessing a microphone from Node on Pi Zero

Question

I am having issues using a microphone in a Node script.

The microphone (a SEEED Array mic) works when running the command line:

arecord -D plughw:1 --duration=10 -f cd -vv ~/rectest.wav

It does not work, however, when called from a node script:

var record = require('node-record-lpcm16');
var fs = require('fs');
var file = fs.createWriteStream('test.wav', { encoding: 'binary' });
record.start({
 sampleRate : 48000,
 verbose : true,
 source: 'plughw:1',
 recordProgram: 'arecord'
}).pipe(file);

This sample script runs fine on my mac, but not on my Rpi Zero.

On Rpi Zero have no error message, the file created is empty.

I have tried a number of things (including combinations of source - 1/1,1/1,0/0,1/0,0) but I am having a hard time finding a way to debug.

I have a Speaker Bonnet from Adafruit connected to the RPI (but get the same error when disconnecting it).

I am running node 8.9.3 and have built 'node-record-lpcm16' with no errors.

Any ideas what of what I could be doing wrong or ideas on how to further debug?

Answer 1

It seems like you have a small mistake regarding the naming of the device parameter. It's called device and not source, changing that should hopefully fix your problem.

ref: https://github.com/gillesdemey/node-record-lpcm16/blob/13b5297c1c982281cdb0407d715d46581fb2c9f2/index.js#L58-L60

Another possible small problem, which might actually not matter in this case, is that you are passing the encoding parameter to createWriteStream. This is meant for telling the stream how to convert JavaScript strings into binary data on disks, but the record module will emit Buffer instances and not strings.

Finally, a small tip is to use the dsnoop module in alsa, so that multiple processes can record at the same time. This might not matter to you though.

Final program:

const record = require('node-record-lpcm16')
const fs = require('fs')
const file = fs.createWriteStream('test.wav')
record.start({
 sampleRate: 48000,
 verbose: true,
 device: 'dsnoop:1,0',
 recordProgram: 'arecord'
}).pipe(file)

Much of my knowledge here comes from writing a Vinyl LP streamer that streams my vinyl records to my Sonos, using a Raspberry PI Zero W. Feel free to check out the source for some inspiration: https://github.com/LinusU/lp-streamer