Too lazy to flip a switch

August 12, 2007 8:25 PM

automatic audio switch: Does it exist? (Two computers, One pair of speakers). (an automatic switch, not a manual one)

I know the manual ones exist, I'm wondering about an automatic switching one, where it switches to the active audio or the most recently turned on audio (exactly like the radio shack RF modulators do when they switch automaticaly between your PS3 and your DVD and your cable tv).

Searching on google/ebay/amazon has not been fruitful. Plenty of manual switches, havent found an auto-switching one.

posted by jak68 to computers & internet (17 comments total)

p.s., for some unknown reason, it posted in tiny font. It looked fine in the preview. sorry about that.
posted by jak68 at 8:27 PM on August 12, 2007

Normal size font over here, by the way.
posted by DMan at 8:27 PM on August 12, 2007

A splitter would work fine, unless they were both playing at once. (font looks fine to me)
posted by tehloki at 8:30 PM on August 12, 2007

ditto the splitter idea. I have a pair of speakers with two inputs. The inputs get summed if both are playing.
posted by pmbuko at 9:18 PM on August 12, 2007

A splitter would be a fine way to do this. There's a chance you'll lose a bit of gain from one source or the other, but the chance it'll cause noticeable degradation in the sound quality is practically nonexistent.

Another option, especially if you might be expanding to more than 2 sources in the future, would be a cheap powered mixer. I have one with 6 inputs that I picked up on ebay for $50, and it works great.

Unless there's a reason you don't want more than one input active at a time, of course, in which case you'll get better help here if you let us know your reasons for wanting that. One trick for reducing hum from computer soundcards: keep the "line in" and mic muted unless you're using them for something.
posted by contraption at 10:12 PM on August 12, 2007

A splitter could damage one or both sources. You can split an output, but never combine an input with a simple wire splitter.

Consider what happens if both are playing at the same time, and at this instant, one waveform is positive while the other is negative: The two outputs see each other as a dead short, and pour current into each other. Whichever device has the weaker driver transistor takes up smoking.

Just use a simple 2-input mixer. If they're both playing at once, you can mute the one you don't want to listen to.

Even simpler, and requires buying nothing: Pipe one computer's line-out to the other computer's line-in, then use the second computer's mixer to adjust the relative levels.
posted by Myself at 10:33 PM on August 12, 2007

A splitter could damage one or both sources. You can split an output, but never combine an input with a simple wire splitter.

While this is technically correct and may have been more of an issue in the before digital electronics and ICs made output protection more commonplace, I have done this many, many times with all sorts of devices with no ill effects. So yeah, I guess it's technically a risk, but it's not something I would buy or build a mixer over.
posted by contraption at 11:04 PM on August 12, 2007 [1 favorite]

I suppose a splitter might work. I'll try that. I had one before but I forgot why I took it off. I do remember being worried about damaging the equipment with it.
The thing about a mixer is that i'm trying to have it be automatic (dont want to lean over and flip any switches at all). Do powered mixers switch automatically?
I'm surprised no one makes a simple auto-switch for audio sources.
Thanks all.
posted by jak68 at 12:06 AM on August 13, 2007

@contraption: Does your 6-input powered mixer switch automatically between sources?
posted by jak68 at 12:07 AM on August 13, 2007

jak68: I think he means you would have both sources running into the mixer and constantly "on", so whatever either device plays gets played through the speakers.
posted by tehloki at 12:38 AM on August 13, 2007

On a mixer all sources are active simultaneously, with each one's level being independently adjustable with a slider. If you wanted to you could simply leave both both sources ramped up, which would in effect give you a "safe" splitter, which you could leave on and never touch if that's what you want.

The reason you see auto-switches for video and not audio is because of a fundamental difference in the way video and audio are transmitted: a video cable carries a "sync" signal that is always there, even if the equipment is just sending a black screen. This signal is easy to detect electronically and can serve as a simple trigger to tell the switch when a device is turned on. In fact, many AV control processors include video inputs that serve no other purpose than giving a reliable reference for device power status.

Audio signals, by contrast, are carried in a much simpler way, where the voltage on the line corresponds more or less directly with the position of the speaker membrane. This means that to an automatic audio switch, a momentary silence in the soundtrack is indistinguishable from the device turning off, and random interference picked up from the air or power supply by cables from a device that's off might be misread as a real incoming signal, causing a false positive. Some subwoofers and amps do have a setting where they're supposed to power on automatically when they detect a signal, but because of these issues they never seem to work satisfactorily.
posted by contraption at 1:20 AM on August 13, 2007 [2 favorites]

I actually have a set of speakers that turns off after 2 minutes or so of "silence". They work pretty well, in fact.
posted by tehloki at 3:48 AM on August 13, 2007

The other reason you see switches for video and not for audio is that a simple summing circuit, which works just fine for combining two audio signals, would completely break the encoding if used to combine two independently generated video signals. You'd get a scrambled meaningless mess instead of any useful kind of mixed video.
posted by flabdablet at 4:30 AM on August 13, 2007

@tehloki @contraption: Oh, I see! Thanks :) So I guess a powered mixer (as opposed to a passive mixer) is the one to get (I suppose a passive mixer would basically be the same as a splitter). Okay, I'll look for a powered mixer on ebay :)
posted by jak68 at 6:56 AM on August 13, 2007

@OP please go the mixer route. you can use an RDL STD-10K googled here to actively combine signals. (about $30 but a professional tool)

as to splitter combiners, this is a bad idea, you will loose 4dB of gain, rolloff the high frequencies above 4K significantly (read: sounds pretty bad) and yes even in the digital age you can cause problems to a driver or op amp... (because the signals in question are still analog and driven by some sort of amplifier circuit)
posted by chasles at 8:18 AM on August 13, 2007

Thanks chasles.
I suppose yet another option is a KVM switch that includes an audio switch (i vaguely remember seeing these on amazon, tho they were VERY pricey). That way when i switch computers the speakers switch too. I'm thinking a 30 buck mixer for now tho.
posted by jak68 at 1:22 PM on August 13, 2007

Just ran across an article about Y-cables backing up my earlier assertion. Contraption's right, it's probably not an issue, but I just thought I'd throw this in here as background.
posted by Myself at 8:42 PM on August 17, 2007