FM Broadcast modulator baseband decimation factor

Does anyone have experience with the FM Broadcast block in Simulink? I keep getting the error "The signal length (number of rows) must be a multiple of the decimation factor:[...]", but the online explanation of what the decimation factor is is not really clear.

Answer 1

[Abhishek Ballaney]

https://in.mathworks.com/help/comm/ref/fmbroadcastmodulatorbaseband.html

[Emilija Lazdanaite]

yes, I've read the documentation, it does not explain what the decimation factor is. It only says "The input length of the audio signal must be an integer multiple of the audio decimation factor." Is the decimation factor then the audioLength/audioSampleRate? Because the number i get as the decimation factor in the error message is not that ratio.

[Quenten Switten]

Have you find the solution on this question?

I ask this because I have the same problem.

Answer 2

[Trey Shenk]

You can find the decimation factor using the comm.FMBroadcastModulator system function "info." Here's a modified version of the Mathworks FM example, with the input truncated so that you need to adjust the length.

audio_data = audioread('guitartune.wav');

audio_fs = 44.1e3; %sampling rate of audio

fs = 240e3; % modulated output sampling rate

fmbMod = comm.FMBroadcastModulator( ...

'AudioSampleRate',audio_fs, ...

'SampleRate',fs);

% truncate audio_data so that it we need to adjust length for demo

audio_data = audio_data(1:661100);

% get the decimation factor

mod_info = fmbMod.info;

dec_factor = mod_info.AudioDecimationFactor;

% zero-pad if needed

zpad_num = dec_factor - mod(length(audio_data), dec_factor);

audio_data = padarray(audio_data, zpad_num, 'post');

% generate modulated signal

sig = fmbMod(audio_data);

% demodulate and listen to confirm settings

fmbDemod = comm.FMBroadcastDemodulator( ...

'AudioSampleRate',audio_fs, ...

'SampleRate',fs,'PlaySound',true);

fmbDemod(sig);