Pure Tone, increasing volume

Does anyone know how to create a pure tone that increases in volume according to a formula? I want to create a sound that increases in volume for 3 seconds, starting from some default value.

Answer 1

[Jan]

1. Create the sound, here a sin wave.
2. Create the shape of the volume as factor with values between 0 and 1.
3. Multiply both:

freq = 8192;
w    = sin(linspace(0, 2000*pi, freq * 3));
sound(w, freq);  % full volume

iniVolume = 0.3;
finVolume = 1.0;
Volume    = linspace(iniVolume, finVolume, length(w));
w2        = w .* Volume;
sound(w2, freq);