From aa9d43f4ae02cdca2ab168e1c2e5fda22ec53d57 Mon Sep 17 00:00:00 2001 From: Christophe Jacquet Date: Mon, 14 Apr 2014 18:56:35 +0200 Subject: [PATCH] Fix in the README --- README.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/README.md b/README.md index 0d0d6cc..57000d8 100644 --- a/README.md +++ b/README.md @@ -116,7 +116,7 @@ The shaped biphase symbol is generated once and for all by a Python program call Internally, the program samples all signals at 228 kHz, four times the RDS subcarrier's 57 kHz. -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: +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: * the Nyquist frequency of the input audio file (half the sample rate) to avoid aliasing, * 15 kHz, the bandpass of the left+right and left-right channels, as per the FM broadcasting standards.