Skip to content

Latest commit

 

History

History
170 lines (112 loc) · 5.96 KB

ADC-LINE-IN.md

File metadata and controls

170 lines (112 loc) · 5.96 KB

How to Use an ADC as a Line-In for Snapcast

This guide explains how to use the Analog-to-Digital Converter (ADC) on a soundcard like the HiFiBerry DAC+ ADC Pro to create a line-in source for your Snapcast server. This allows you to stream audio from any analog device (e.g., a turntable, CD player, or phone) to all of your Snapcast clients.

How It Works

The audio flows from your analog device through a chain of software components on the server:

Analog Source → ADC Input → arecord (Capture) → Named Pipe (FIFO) → Snapserver → All Snapclients

Prerequisites

  • A working Snapcast server running on a Raspberry Pi.
  • A soundcard with an ADC, like the HiFiBerry DAC+ ADC Pro, physically installed.
  • The driver for your soundcard must be activated and working (see the soundcard docs).
  • An analog audio source connected to the "Line In" on your soundcard.

Step 1: Find Your Capture Device

First, we need to identify the correct ALSA device name for your soundcard's input.

arecord -l

Look for your card in the output. The device name will be in the format card X: CARDNAME [Device Long Name], device Y: .... You need the CARDNAME from this list.

For the HiFiBerry DAC+ ADC Pro, it will look something like this:

**** List of CAPTURE Hardware Devices ****
card 1: DACPLUSADCPRO [snd_rpi_hifiberry_dacplusadcpro], device 0: HiFiBerry DAC+ ADC Pro HiFi-0 [HiFiBerry DAC+ ADC Pro HiFi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

From this, we can construct the full device name. The most reliable method is to use the card and device index numbers.

  • Card Index: card 1 -> 1
  • Device Index: device 0 -> 0

The ALSA device name is hw:1,0. Note this down, as you will need it later.

Step 2: Create a Named Pipe

A named pipe (or FIFO) is a special file that acts as a buffer. We will write the captured audio into this pipe, and Snapserver will read it from the other end.

sudo mkfifo /tmp/snap-line-in

Step 3: Add the Line-In Stream to Snapserver

Now, tell Snapserver to create a new stream that reads from the pipe we just created.

  1. Edit the Snapserver configuration:

    sudo nano /etc/snapserver.conf

  2. Add a new [stream] source. Add this block to the file, alongside your existing AirPlay and Spotify streams.

    [stream]
source = pipe:///tmp/snap-line-in?name=Line-In&sampleformat=48000:16:2
    • name=Line-In: This is the name that will appear in your Snapcast client apps.
    • sampleformat=48000:16:2: This tells Snapserver to expect CD-quality stereo audio (48kHz sample rate, 16-bit depth, 2 channels).

Step 4: Create a Service to Capture the Audio

To continuously capture audio from the ADC and feed it into the pipe, we'll create a systemd service.

  1. Create the service file:

    sudo nano /etc/systemd/system/snap-line-in.service

  2. Add the following configuration. This service will run the arecord command constantly. IMPORTANT: Replace hw:CARD=DACPLUSADCPRO,DEV=0 with the device name you found in Step 1.

    [Unit]
Description=Snapcast Line-In Capture Service
Wants=snapserver.service
After=snapserver.service

[Service]
Type=simple
# IMPORTANT: Change the -D device to match your hardware from 'arecord -l'
ExecStart=/usr/bin/arecord -D hw:1,0 -f S16_LE -r 48000 -c 2 /tmp/snap-line-in
Restart=always2 /tmp/snap-line-in
Restart=always
RestartSec=1

[Install]
WantedBy=multi-user.target

Step 5: Enable and Start Everything

Finally, enable the new service and restart Snapserver to apply all changes.

# Reload systemd to recognize the new service
sudo systemctl daemon-reload

# Enable the service to start on boot and start it now
sudo systemctl enable --now snap-line-in.service

# Restart snapserver to load the new stream configuration
sudo systemctl restart snapserver

Step 6: Test It!

  1. Open your Snapcast control app (like Beatnik Controller or Snapweb). You should now see a new stream named "Line-In".
  2. Select the "Line-In" stream for one of your client groups.
  3. Play some audio from your connected analog source.

The audio should now be playing across your selected Snapcast clients, perfectly in sync!

Troubleshooting

Service Fails to Start ("Start request repeated too quickly")

This error means the arecord command in your service file is failing immediately. Here’s how to find the real error and fix it.

1. Check the Detailed Logs

Run this command to see the exact error message from arecord:

journalctl -u snap-line-in.service

2. Common Causes and Fixes

  • The Error: arecord: main:831: audio open error: No such device or Cannot get card index for...

    • Cause: The device name in your command (-D hw:1,0) is incorrect.
    • Fix: Run arecord -l again and carefully check the card X and device Y numbers. Correct the hw:X,Y value in your /etc/systemd/system/snap-line-in.service file.

  • The Error: arecord: main:831: unable to open audio device: Device or resource busy

    • Cause: Another application is already using the sound card's input.
    • Fix: Find and stop the other process. You can check what's using your sound devices with sudo fuser -v /dev/snd/*.

  • The Error: Rate 48000Hz not available for capture or Unsupported format

    • Cause: Your sound card doesn't support the exact sample rate or format requested.
    • Fix: Try a different sample rate (e.g., -r 44100) or format (e.g., -f S32_LE) in your service file's ExecStart line. Remember to also update the sampleformat in your /etc/snapserver.conf to match!

After making any changes to the service file, remember to reload systemd and restart the service:

sudo systemctl daemon-reload
sudo systemctl restart snap-line-in.service