Modulation of a signal

[labosluna]

Hi friends. I am new with audacity and I would like to make an amplitude modulation of a wave, using the formula my_wave * cos(2pif*t)
Does anyone know how to do it in audacity. It is really easy to do in other software like Goldwave, bit I need to do this in Audacity. Thankls in advance

[Trebor]

@labosluna

It is really easy to do in other software like Goldwave, bit I need to do this in Audacity.

There is an “expression generator” plugin for Audcaity, (which is similar to the generator in GoldWave)

Expression Generator

Here’s a plug-in written in response to this forum topic: https://forum.audacityteam.org/t/generating-f-x-type-wave-forms/45194/1 The idea of the plug-in is that an arbitrary function “f(x)” may be entered, and the plug-in will generate a waveform by evaluating the expression for a given range of “x”. This version of the plug-in takes its default expression from dmonty’s initial enquiry: x^3 * e^(sin ( x * 3)) * 0.00001 I’m sure some user’s would like to be able to enter the expression in th…

[labosluna]

Thanks Trebor
I have tested this plugin
However, whay I need is to do the amplitude modulation of a wave that I have (let’s say) in the window “Audio 1”. Thius is a wave sampled 44100hz.
The equation is just “my wave” * cos (2pif*t) , f is the carrier (let’s say 10KHz).
Can I do this with this expresion generator, or do you klnow any other way? ASppreciate your answer

Thanks!!!

[Trebor]

@labosluna

… amplitude modulation of a wave … carrier (let’s say 10KHz).

If this is a “silent subliminal” project I think I can save you some time …

"Silent Subliminal" messages revealed

[labosluna]

I have just discovered how to do it. It is so simple: Nyquist command:

(mult *track* hzosc(30000))

30000 is the cariier frequency and *track* the currect track selected

Very strange that no one knew how to do so simple thing, and very strange that this command is not present in the most popular plugins is audacity

Thanks for your answer

[Trebor]

@labosluna

(mult *track* hzosc(30000))

You’ve put a bracket in the wrong place, it should be …

(mult *track* (hzosc 30000))

Typical audio electronics (e.g. laptops, mp3 players, headphones, speakers, mobile phone) are not capable of reproducing 30000Hz.
Typical digital audio files (mp3, YouTube videos) are not capable of storing 30000Hz.
No human can hear 30000Hz.

If you apply that code to audio with a sample-rate of <60kHz you may hear inverted (scrambled) audio due to aliaising.

[labosluna]

You’re right, the brac ket is placed as you say

I realize that 30khz is out of the audible bandwidth. This is the reason because I used that, because I wanted to multpiplex several audio tracks modulated in amplitude, different carriers (30kHz, 50kHz, 70KHz) In that way all them can be mixed in the same track, no one can be listened, and they can be demodulated

This is an exercise I am doing in the Univiersity with my students

It was frustated not to be able to do with audacity, but finally I succeded.

Regards

[Trebor]

@labosluna

70KHz

You’re going to need an unusually high sample-rate of at least twice that frequency.
and that code (full AM modulation) will generate a redundant inverted version, which is a waste of bandwidth.