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Audio Input: quarter sample rate heterodyne for mono signals

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f4exb
2020-11-13 19:55:09 +01:00
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plugins/samplesource/audioinput/readme.md
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@@ -38,9 +38,9 @@ A control to set the input volume. This is not supported by all input audio devi
<h3>7: Channel Map</h3>
This controls how the left and right stereo audio channels map on to the IQ channels.
This controls how the left and right audio channels map on to the IQ channels.
* I=L, Q=0 - The left audio channel is driven to the I channel. The Q channel is set to 0.
* I=R, Q=0 - The right audio channel is driven to the I channel. The Q channel is set to 0.
* I=L, Q=R - The left audio channel is driven to the I channel. The right audio channel is driven to the Q channel.
* I=R, Q=L - The right audio channel is driven to the I channel. The left audio channel is driven to the Q channel.
* 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.