envelope слагаш ли?

The PC speaker is normally meant to reproduce a square wave via only 2 levels of output (the speaker is driven by only two voltage levels, typically 0 V and 5 V). However, by carefully timing a short pulse (i.e. going from one output level to the other and then back to the first), and by relying on the speaker's physical filtering properties (limited frequency response, self-inductance, etc.), the end result corresponds to intermediate sound levels. This effectively allows the speaker to function as a crude 6 bit DAC,[5] thereby enabling approximate playback of PCM audio. This technique is called pulse-width modulation (PWM) and is notably used in class D audio amplifiers.

With the PC speaker, this method achieves limited quality playback; the quality depends on a trade-off between the PWM carrier frequency (effective sample rate) and the number of output levels (effective bitrate). The clock rate of the PC's programmable interval timer which drives the speaker is fixed at 1,193.18 kHz.[3] This relatively low modulation frequency limits the resolution and produces poor but recognizable audio.[6]

Малкото синче на програмист пита баща си:
- Тате, какво са това "ноти"?
- Ъъ-ъ-ъ... Това е нещо като MIDI файл, само че на хартия.

Ето и нещо за размисъл: http://newt.phys.unsw.edu.au/jw/notes.html

Иначе вариант с филтри ми е малко сложен, освен ако не са чисто софтуерни. Някакъв твърди, че като се променя запълването се променяла амплитудата при пиезотата.