kopia lustrzana https://github.com/F5OEO/PiFmRds
Fix in the README
rodzic
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@ -116,7 +116,7 @@ The shaped biphase symbol is generated once and for all by a Python program call
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Internally, the program samples all signals at 228 kHz, four times the RDS subcarrier's 57 kHz.
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The FM multiplex signal (baseband signal) is generated by `fm_mpx.c`. This file handles the upsampling of the input audio file to 228 kHz, and the generation of the multiplex: unmodulated left+right signal (limited to 15 kHz), possibly the stereo pilot at 19 kHz, possibly the left-right signal, amplitude-modulated on 38 kHz (suppressed carrier) and RDS signal from `rds.c`. Upsampling is performed using a zero-order hold followed by an FIR low-pass filter of order 60. I use a sampled sinc windowed by a Hamming window. The filter coefficients are generated at startup so that the filter cuts frequencies above the minimum of:
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The FM multiplex signal (baseband signal) is generated by `fm_mpx.c`. This file handles the upsampling of the input audio file to 228 kHz, and the generation of the multiplex: unmodulated left+right signal (limited to 15 kHz), possibly the stereo pilot at 19 kHz, possibly the left-right signal, amplitude-modulated on 38 kHz (suppressed carrier) and RDS signal from `rds.c`. Upsampling is performed using a zero-order hold followed by an FIR low-pass filter of order 60. The filter is a sampled sinc windowed by a Hamming window. The filter coefficients are generated at startup so that the filter cuts frequencies above the minimum of:
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* the Nyquist frequency of the input audio file (half the sample rate) to avoid aliasing,
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* 15 kHz, the bandpass of the left+right and left-right channels, as per the FM broadcasting standards.
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