What is power draw difference: 3,5mm amplified audio output vs. USB PCM output?
 

Hi,

Do you know how much do these scenario's generally create power draw?
A. Amplified audio playback to headphones through 3,5mm port in N900 for example.
B. USB LPCM audio data output.

I'm interested in this since N9 might have USB host mode feature, which would open possibilities for USB audio output.

I'm wondering what kind of hit USB audio output might put on battery, if it's more or less than amplified line output to headphone port.

Re: What is power draw difference: 3,5mm amplified audio output vs. USB PCM output?
 

USB audio will draw more unless your USB headphone/soundcard/etc is self-powered. Can't tell exact draw in either case because that depends on the actual equipment connected (impedance, USB electronics power draw, etc).

Re: What is power draw difference: 3,5mm amplified audio output vs. USB PCM output?
 

Headphones draw roughly 20 mW (generic run of the mill, can go as high as 2000 but not in N900). USB draw varies (generically speaking) from 100 mA@5V (500mW) to 500 mA (2500mW), depending on what the device requires/requests.

So, generically speaking, USB draws more. It is possible, however, as attila77 said, to have self-powered USB, in which case the data link draw would be even lower than headphones.

When playing audio, your biggest draw is the player software, decoder, audio layer, etc all keeping CPU up.

Also, if you have an external amplifier, low volume audio (down to line level, maybe with added electronics) would give you the longest play time. But then again, if you plan on carrying extra weight an external emergency pack will likely be more useful and not always-connected. Cheaper, too, most likely.

Re: What is power draw difference: 3,5mm amplified audio output vs. USB PCM output?
 

Keeping the USB controller powered seems to use 80-150mA though... So my bet is on headphone out using less power.

Re: What is power draw difference: 3,5mm amplified audio output vs. USB PCM output?
 

A USB device can negotiate for 100-500mA of current - but don't need to draw the negotiated current.

But my vote is for the headphones alternative consuming less. It's a quite small amplifier that is used.

The main question is the consumption of the USB hardware and how much "sound card" that needs to be enabled when sending out the sound digitally or through the analogue headphone connector. Even a small difference in CPU load will also matter greatly.