How to mix multiple audio signals in Matlab?

Hello, I am trying to mix 3 audiofiles in matlab.

The code is as follows.

[guitar, fs_g] = audioread('guitar.wav');

[bass, fs_b] = audioread('bass.wav');

[drums, fs_d] = audioread('drums.wav');

guitar_10s = guitar(1:fs_g*10);

bass_10s = bass(1:fs_b*10);

drums_10s = drums(1:fs_d*10);

mix = guitar_10s + bass_10s + drums_10s;

sound(mix, 44100)

I read in 3 audio files which are 16 bit 44.1kHz wav files.

They are stored as matrices with datatype: double precision normalized.

I cut them at 10 seconds from the beginning.

When I simply add 3 files that are cut, I see something strange when I look into 'mix'.

I see data that exceed 1 or -1.

Is it okay to just arithmetically add audio data that is normalized to make a summed mix?

Also, when I look into the data, It does not look precise at all compared to the data when I read the audiofiles in 'native' datatype. The data -1 <= y <= 1 in double precision doesn't seem like it actually is. Is there something wrong?

Answer 1

[Star Strider]

It is somewhat difficult to follow your code (and I cannot run it since my version of MATLAB can only run actual code, not images of code). However if you want to be certain that the sound remains between [-1 1], the easiest way would be to normalise it.

Example —

t = linspace(0,1,44100);
y = sin(2*pi*t*500)*2;

figure
plot(t,y)

y = y/max(abs(y));                              % Normalise
sound(y, 44100)

Here, ‘y’ is originally ±2, however when normalised, it is ±1. That is likely the easiest way I can think of to be certain it meets that criterion.