optical out sound card for linux?

[phiscock-g851W1bGYuGnS0EtXVNi6w at public.gmane.org]

> High impedance means it requires a higher voltage to get the same amount
> of sound generated.

Correct.

> If you can't generate that amount of voltage, then
> you won't get the desired sound or you may get distorsion because the
> amplifier can't keep up with the power demand.

Well, not exactly. The operator turns up the volume -> the output voltage
increases -> this leads to 'clipping' before the desired effect (louder
sound) is achieved. The power supply rails of the output amplifier set the
maximum output voltage, and when the output tries to exceed those, the
output voltage limits. On a scope (such as our beautiful Syscomp DSO-101
which we manufacture, shameless plug ;) you would see flat tops at the
extremes of a sine wave. These flat tops represent gross distortion.

> So yes they draw less current _at a given voltage_,

Correct

> but that simply
> means they desire a higher voltage in the first place.
             ^^^^^^
I'd say that the speaker or earphone *requires* a larger voltage to drive
sufficient current through the higher resistor to cause a given output
sound power.

As a historical note, domestic loudspeakers are nominally 8 ohms
impedance. Car loudspeakers have tended to be 4 ohms impedance because the
available supply voltage is limited by the car battery voltage. Lower
impedance means that the available voltage can drive a larger current
through the speaker, thereby creating a louder noise.

The basic point that Lennart makes - that a sound card was meant to drive
powered loudspeakers (which require next to no input signal) or high
impedance headphones (ditto) is correct. You can't drive a loudspeaker or
low impedance headphones with that signal: you need a power amplifier.

-- 
Peter Hiscocks
Syscomp Electronic Design Limited, Toronto
http://www.syscompdesign.com
USB Oscilloscope and Waveform Generator
647-839-0325

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