sdrangel/plugins/samplesource/audioinput

Audio input plugin

Introduction

This input sample source plugin gets its samples from an audio device.

Interface

The top and bottom bars of the device window are described here

1: Start/Stop

Device start / stop button.

• Blue triangle icon: device is ready and can be started
• Green square icon: device is running and can be stopped
• Magenta (or pink) square icon: an error occurred. In the case the device was accidentally disconnected you may click on the icon, plug back in and start again.

2: Device

The audio device to use.

3: Refresh devices

Refresh the list of audio devices.

4: Audio sample rate

Audio sample rate in Hz (Sa/s).

5: Decimation

A decimation factor to apply to the audio data. The baseband sample rate will be the audio sample, divided by this decimation factor.

6: Volume

A control to set the input volume. This is not supported by all input audio devices.

7: Channel Map

This controls how the left and right audio channels map on to the IQ channels.

• Mono L - Real samples are taken from the left audio channel and are heterodyned by the fourth of the sample rate (fs/4) to obtain complex samples. Therefore the spectrum of the complex baseband is centered at the fourth of the sample rate (fs/4). As per Nyquist rule only a bandwidth of half of the sample rate (fs/2) is available for real signals. Frequencies outside the [0, fs/2] interval are artefacts and can be eliminated by decimating by a factor of 2.
• Mono R - Same as above but takes the right audio channel for the real signal.
• I=L, Q=R - The left audio channel is driven to the I channel. The right audio channel is driven to the Q channel for a complex (analytic signal)input.
• I=R, Q=L - The right audio channel is driven to the I channel. The left audio channel is driven to the Q channel for a complex (analytic signal)input.