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One thing that's not clear from the article - are external headphones required for this to work? Can this not be done with the built-in speakers?
by mthoms 10y ago
One thing that's not clear from the article - are external headphones required for this to work? Can this not be done with the built-in speakers?
- justinclift 10y agoIt seems like something that would work for built-in speakers too. They're driven by the same audio codec chips (eg realtek), but wired directly instead of through an external socket.
- janci 10y agoI think the opposite. Speakers are driven by an amplifier that will not let the audio in reverse, even if the soundcard output was switched to act as an input.
- wallacoloo 10y agoBut might there be sufficient coupling between the amplifier's output and its input, such that driving the output pins via speaking into the speaker can produce a voltage on what is usually the input line to the amplifier? I suspect it may be possible, depending on what the firmware allows - amplifier circuitry often utilizes feedback in some form or another, which is essentially coupling the output to the input. And even if the amplifier is powered off, there's bound to be capacitive coupling between the input/output lines, but that's probably too small to be useful.
- qb45 10y agoThis could totally work in this kind of circuit for example: https://en.wikipedia.org/wiki/Operational_amplifier_applications#Inverting_amplifier https://en.wikipedia.org/wiki/Operational_amplifier_applicat... While I have seen a soundcard using two such inverting stages in series for headphone output, in laptops dedicated chips are more common which probably don't have such strong coupling. But better safe than sorry if the NSA is after you :)
- justinclift 10y agoInteresting point, hadn't considered that. Sounds like it'll be one of those "implementation dependent" things then, and someone into this kind of thing should probably investigate.
- upofadown 10y agoUnlikely. There is going to be some sort of audio amplifier in the way that won't transfer signals very well in reverse. Even if it is built in to the audio chip there would be little point in allowing that output to be an input.