Help! I'm getting audio underruns or overruns!

Audio underruns

There may be multiple causes of this:

You run out of Internet uplink bandwidth

OpenWebRX typically requires 200 kbit/s uplink per client. If you run it from a home Internet connection, and multiple clients are connected, you may run out of the uplink bandwidth your ISP allows.

Possible solutions:

• Reduce the FFT size (fft_size in config_webrx.py), by which you can decrease the bandwidth usage to about 100 kbit/s per client.
• Reduce the maximum allowed number of clients to a safe value, at which no lags occur, by the max_clients setting in config_webrx.py.

You run out of CPU time

I mean, you set a quite high sample rate (multiple Msps), and the CPU cannot handle that. Sometimes it only happens when multiple clients connect simultaneously: when the N-th connection is made, the audio starts to lag for everyone. You can also observe around 100% CPU usage at the status bar.

You can try several things:

• Reduce the maximum allowed number of clients to a safe value, at which no lags occur, by the max_clients setting in config_webrx.py.
• Reduce the sampling rate of the SDR hardware (samp_rate in config_webrx.py).
• You can also reduce the FFT size (fft_size), although it has less impact on CPU usage as it is calculated only once.

For some benchmarks please see this page.

See also Optimizing OpenWebRX for speed.

Internal buffering problem within OpenWebRX

If nothing helps, you can try to increase the client_audio_buffer_size in config_webrx.py.

Audio overruns

In reality, your SDR receiver is not working at the sampling rate you set

You should try another value for samp_rate.

Internal buffering problem within OpenWebRX

If nothing helps, you can try to alter the client_audio_buffer_size in config_webrx.py.