Re: Line level audio

[Nigel Orr <nigel.orr@xxxxxxx>]

At 10:09 06/11/98 GMT, you wrote:

>I've been following the distributed audio discussuion and I have a
couple
>of (hopefully) simple questions.

I've not (yet) had to solve similar problems in the house, but I can
certainly help from the pro audio side of things...

>I would like to link my computer sound card (in an upstairs office) to
>my HiFi (downstairs). For simplicity I will be running the cable up to
>the loft across the roof space and down a convenient duct to the
kitchen,
>through the wall into the lounge, a distance of about 25m. Is this
>possible without booster electronics ?

Unbalanced, high impedance- ie cheap equipment- will sound a bit muffled
(due to cable capacitance), and likely to pick up mains hum (due to
unbalanced-ness)
Balanced, low impedance- should be fine up to a km or two, but you'll need
to buy or build converters from typical hi-fi levels.

If you can't find anything suitable ready-made, try a transformer- 10:1
step down at the sending end (so the cable between is low level, low
impedance, isolated), and 10:1 at the other end.  Even lower ratios would
probably be fine- 10:1 will give you 1/100th of the impedance.  Use a
decent audio transformer, not a mains one... you should be able to get
something half-reasonable for about a fiver.

>What kind of cable should I use
>and how much should I expect to pay ?

I'm planning to use UTP to carry everything- about 50p per metre in small
quantities, about 75 quid for 1000ft reels.

>  I do not have any desire (or see
>a future requirement for) video signals but I may want to add ethernet
>capabilities, I do not mind installing an additional cable for this at
>a later date.

If you just want audio, and no flexibility, you could probably use a
cheaper twin screened cable or multicore- Belden, Van Damme and Canare are
all good audio cable manufacturers, but I expect UTP should do this job
fine- you'd still need balancing and impedance conversion for any cable.

>Has anyone used a clip on radio mic instead of multiple mics in each
room
>for voice control ?  My local Tandy was selling them off cheap and it
set
>me thinking ...

The distortion and noise from a cheap radio mic might cause problems for
voice recognition- I dunno, and suspect you'd just have to try it.  Cheap
radio mics would probably work OK throughout a typical home.  Any radio mic
would be very susceptible to someone jamming or controlling the system
externally.  Cheap radio mics tend to go through batteries fast, so you'd
want one with good squelch so you can turn the transmitter off when you're
not speaking.

Nigel (who would normally run a mile from a cheap radio mic, but just this
once, it might have a use...)

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