How to impliment a Single Sideband Suppressed Carrier Modulator with an audio file as input?

I have been given an audio signal which I imported into MATLAB using audioread. I have obtained fs and can naturally plot the time domain signal. After an FFT the frequency domain can easily be plotted.

My Question is how do I take this signal as input and modulate it using SSB-SC modulation in MATLAB? I believe I first have to create a DSB and then filter the sidebands using filters, but I am also unsure of how to create the DSB, the filter I may be able to create. Any suggestions will be greatly appreciated.

Answer 1

[Hari]

Hi Rhyston,

I understand that you want to modulate an audio signal using Single Sideband Suppressed Carrier (SSB-SC) modulation in MATLAB. You are seeking guidance on creating a Double Sideband (DSB) signal and filtering the sidebands for SSB modulation.

I assume you have already imported your audio signal and have access to its sampling frequency (fs).

In order to perform SSB-SC modulation on your audio signal, you can follow the below steps:

Create the DSB Signal:

Multiply your audio signal with a carrier signal to create a DSB signal. Use a cosine function for the carrier.

t = (0:length(audioSignal)-1)/fs; % Time vector
fc = 10000; % Carrier frequency, adjust as needed
carrier = cos(2*pi*fc*t);
dsbSignal = audioSignal .* carrier;

Apply Hilbert Transform:

Use the Hilbert transform to create an analytic signal, which helps in isolating the sidebands.

analyticSignal = hilbert(dsbSignal);

Generate the SSB Signal:

Use the real part of the analytic signal to create the SSB signal. This effectively removes one of the sidebands.

 ssbSignal = real(analyticSignal);

Filter the Signal (if needed):

If further filtering is necessary to isolate a specific sideband, design and apply a bandpass filter.

 % Example: Design a bandpass filter using "designfilt"
 bpFilter = designfilt('bandpassfir', 'FilterOrder', 20, ...
     'CutoffFrequency1', fc-500, 'CutoffFrequency2', fc+500, ...
     'SampleRate', fs);
 filteredSignal = filter(bpFilter, ssbSignal);

Plot the SSB Signal:

Visualize the SSB signal in the time domain to verify the modulation process.

 plot(t, ssbSignal);
 xlabel('Time (s)');
 ylabel('Amplitude');
 title('SSB-SC Modulated Signal');

Refer to the documentation of "hilbert" function to know more about creating analytic signals: https://www.mathworks.com/help/signal/ref/hilbert.html

Refer to the documentation of "designfilt" function for filter design: https://www.mathworks.com/help/signal/ref/designfilt.html

Hope this helps!