From: "Michael R. Kesti"
Subject: Re: audio line specifications
Date: Wed, 04 Dec 2002 09:06:01 -0800
Organization: MK Associates
X-Mailer: Mozilla 4.7 [en] (Win98; I)
Mickael Lorgeoux wrote:
>I'm looking for analog audio line signal specification document. I want
>to have the levels values, the load requirement, etc...
>Is there an international standard document for audio line? I mean an
>equivalent of video NTSC or PAL standard documents.
There are no such standards for audio. Instead, most equipment, both
consumer and professional, is designed to a rather loose set of conventions.
For consumer equipment these include:
o Format: unbalanced using a single conductor for the signal that is
referenced to a grounded shield.
o Impedance: voltage transfer techniques are used with source impedances
in the 100's of ohms and load impedances of 10's of thousands of ohms.
o Level: nominally -10 dBV (10 decibels below 1 volt, or 0.316 volts)
with 10 to 25 dB of headroom for peaks above that level.
Pro equipment conventions include:
o Format: balanced using a two signal conductors of opposite polarity
that are not referenced to a grounded shield.
o Impedance: power transfer techniques using matched source and load
impedances of 600, 300, or 150 ohms used to be common and are still
sometimes used, but voltage transfer techniques with source impedances
in the 100's of ohms and load impedances of 10's of thousands of ohms
are far more common in modern equipment.
o Level: nominally +4 dBm (4 decibels above 1 milliwatt dissipated in the
load impedance) for power transfer and +4 dBu (4 decibels above 0.775
volt, or 1.23 volts) for voltage transfer, with 10 to 25 dB of headroom
for peaks above those levels. (Note that 0.775 volts across 600 ohms
results in a dissipation of 1 milliwatt.)
Michael Kesti | "And like, one and one don't make
| two, one and one make one."
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