[sdiy] Audio Levels

[Don Tillman]

   Date: Thu, 6 Sep 2001 12:05:51 -0500 (CDT)
   From: Justin Herrmann <herrmann at eecs.ku.edu>

   I've been wondering for awhile, what's the impedance and voltage
   range for mic, guitar, line level, and the audio level synth
   modules use?

These numbers vary a lot depending on the specific pieces of equipment
and the technology.  

Microphone level is roughly around -40 dBu.  Standard microphone
impedance is 600 ohms balanced, and a microphone input on a mixer is
typically about 5.0K ohms balanced.

The maximum guitar output is about 2.0 volts peak to peak.  (Some
basses can put out 8.0 volts peak to peak if you really slam them.)
The output impedance varies greatly with frequency, but it's
considered bad form to load down a guitar signal with anything lower
than a 1.0M ohm impedance.

Line level is sometimes considered -10 dBu,sometimes 0 dBu, depending
on the mood.  Load is 10K to 30K ohms.

Standard power amp line level is +4 dBu, 10K to 30K ohms, but some
hifi amps vary from that a lot.

There are two schools of thought about audio levels for synth modules.
Moog, Buchla and others use a 0 dBu level to be compatible with other
studio gear.  ARP and others design things so there is no
differentiation between audio and control signals, so the audio
signals end up being +/- 5.0 volts.

I use Mackie mixers a lot, and their web site is an excellent
reference for this sort of thing.

  -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com