Re: sound recording with Fedora 11

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Kevin Kempter:
>> He wants to record some of his band sessions, we tried using 'sound recorder' 
>> and plugging the output of his mixer into the mic input on the laptop.

In most cases, mixers have a high signal level output for connecting to
line inputs, and the mic input will be over driven by 100 to 1000 times
more voltage than it wants.  So use the line input, externally attenuate
the signal going to the mic input, or use an external sound device.

> most mic inputs were of high impedance as it was cheaper to make a high
> impedance mic than a low impedance. today a lot of that has changed and many
> mics are now dynamic low impedance.

*Most* microphones, domestic and professional, have been, and nearly
always have been, low impedance.  Very old school thought was to match
the input stage impedance to the microphone impedance, later on most
manufacturers moved to using high impedance input stages.

High impedance microphones only work well into high impedance input
stages, most low impedance microphones will work into either, and there
are some other benefits in using high impedance inputs.  There are also
some benefits in using low impedance input stages, but they're not
usually an issue.  And it's only a few microphones that require a low
impedance stage.

> if you are feeding a high impedance input with a low impedance line output,
> you can get poor sound quality.

While that's true, their problem is far more likely to do with signal
level differences.  i.e. A microphone level may be .0001 to .001 volts,
compared to a line level which may be .1 to 2 volts, nominally.  There
are some very large variations in nominal mic and line levels.

Computers often have lousy built in audio hardware, and it's working in
a very electrically noisy environment.  Plugging in an external sound
device, such as via the USB ports, can make a large improvement to the
sound quality.  It can also help in giving you larger, robust,
connectors, and perhaps the connectors that you want (e.g. XLR, RCA, or
quarter-inch jacks, rather than those unreliable 3.5 mm jacks).

If you do use the computer's own sound hardware, you really want to use
the line level.  It'll probably be the right signal level, and the
quietest input on the computer.  The microphone will have a large amount
of gain, making it noisier, and will probably have DC on the socket for
powering the average computer microphone.  You don't want DC going to
anything else, it can wreck things.  Or, at the very least, make awful
noises if the connection is not tight.

Tim (who works in television and video production).

[tim@localhost ~]$ uname -r

Don't send private replies to my address, the mailbox is ignored.  I
read messages from the public lists.

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