If a USB interface is bus-powered,

I don't think so. There is only so much power the bus can provide though. Some devices have a separate power supply just in case.
 
Any interface that is bus powered is only drawing additional current from the computer's power supply and is limited to 500 mA at 5 vDC.

No compute cycles are taken away from the cpu due to bus powering.
 
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Ah! Thank you. I suppose that it's safe to assume that an interface like the Scarlett, which has an external power supply, requires more juice than the bus can supply.
 
Eleanor Fudd said:
Ah! Thank you. I suppose that it's safe to assume that an interface like the Scarlett, which has an external power supply, requires more juice than the bus can supply.
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That's most likely the case.
A computer's power supply can be also be noisy and many interface designers prefer to control the quality of the power by using a non-bus powered supply.
 
jaygee said:
That's most likely the case.
A computer's power supply can be also be noisy and many interface designers prefer to control the quality of the power by using a non-bus powered supply.
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I see. I suppose it's one fewer possible complication. It's too bad, though, as the NI6
seems a very nice package. I think I'd rather spend on an interface with an external power source.

Thanks again.
 
I don't know about USB, but I've used the Firestudio Mobile, which is a bus powered Firewire interface. It comes with an external power supply, but I've never really needed it. It doesn't put any stress on my laptop energy wise, and it doesn't slow it down or anything either if that's what you meant. I think the external supply might be necessary when using phantom power? I don't know, I have external pre amps for that so I've never tested that theory out.
 
Although the USB standard states that 5VDC at 500mA will be available on the bus, this is not always guaranteed in practice. Some chip-sets do not seem to provide the full current rating. For that reason, some form of external powering is useful.
 
PRHunt said:
Although the USB standard states that 5VDC at 500mA will be available on the bus, this is not always guaranteed in practice. Some chip-sets do not seem to provide the full current rating. For that reason, some form of external powering is useful.
Click to expand...

I've decided to lean in that direction. Thanks.
 
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