From the comments:
So, how does it get louder without getting higher pitch? Wouldn't more energy make it faster and higher pitch, not louder? Or .... what am I missing? ------------- is the speed of the diaphragm expansion per pulse constant with varying torque dependent on voltage? Because otherwise a speaker wouldn't get louder it would just reach it's destination faster and get all distorted sounding and chipmunky (sic)?
You are missing some basic physics. Pitch is the frequency of oscillation of a sound wave. Volume is the amplitude (size) of the oscillation.
A microphone converts sound pressure waves into an analogous signal. That means the voltage waveform will vary in proportion to the instantaneous sound pressure. The electrical signal can be amplified to drive a loudspeaker directly or it may be sampled and stored digitally at a rate high enough to give enough fidelity when converted to analog again.
A loudspeaker converts (a higher powered) electrical waveform to sound. Again, this is an analog conversion. The pitch is the frequency of oscillation of the electrcial signal and the resultant sound wave. Volume is the amplitude (size) of the oscillation.
Get a frequency generator app for your phone, plug it into your amplifier and put your fingers lightly on the speaker cone as you vary pitch and volume. You might get best touch results at low frequencies.
If digital electronics can only vary the pulse-width of their ones and zeroes, how can they ever hope to send amplitude data to a speaker?
Pulse-width modulation with low-pass filtering allows any voltage to be recreated between minimum and maximum output voltage of the amplifier.
Figure 1. A PWM amplifier output reproduction of a sinewave. Source: Vanatoo.
It should be clear from the image above that to reproduce the sinewave at full volume the PWM needs to vary from clost to 0% to 100%. To reproduce the sinewave at 40% volume the PWM would be limited to 30% to 70% modulation.
It's obviously more complicated than one signal, because it would be multitone singular-volume, so it must have parallel channels, and a way of requesting amplification, right?
I don't know what you mean by "multitone singular-volume" but I'll assume that you mean broad-spectrum sound such as music or speech. All sound impinging on your ear is the instantaneous sum of sound pressure waves so to recreate this waveform we need to PWM at sufficiently high frequency to be able to generate the highest frequencies of interest. There is no "requesting amplification". We just reproduce the original waveform as best as the chosen hardware allows.
... so you would only be able to control pulse-width was my thinking, unless you had a DAC, and a way to tell it it produce more voltage per pulse?
The point of PWM is that you can do DAC simply with an on-off digital output and low-pass filter. The filtered output voltage is simply proportional to the pulse width.
See the linked article for more information.
There is however, a such thing as: 00001111 or 010101010, the first being low frequency and the second being high frequency, although, again, there's no change in amplitude, not via digital signal alone.
No, this is incorrect.
- The binary values determine the PWM pulse width.
- '00001111' = decimal 31. On an 8-bit (256 steps) system this would result in a pulse width of 31/256 = 12.1% pulse width. On a 5 V digital system this would result in an average voltage of 0.605 V.
- '10101010' = decimal 170. On the 8-bit system the pulse width would then be 170/256 = 66.4% and the average voltage would be 3.32 V.
The data is stored in bytes or words. These bytes or words are converted to pulse widths by the controller hardware. The pulse widths determine the average voltage. By updating fast enough we can reproduce a high-fidelity version of the original analog signal.