On 11/19/2010 10:09 AM, Randy Yates wrote:
What I meant to ask is if
there is a standard way to map the full-scale output of a DAC
(or input of an ADC) to a specific voltage voltage level.
Nope.
There are a few conventions, however, but mostly there's things that
you choose for yourself, not a standard to which a manufacturer
adheres. Back when people had VU meters and digital recorders had
readable meter scales and an adjustable input level control, there was
often a mark typically somewhere between -16 and -20 dBFS on the
digital meter that was the recommended point corresponding to 0 VU.
And 0 VU correspondings to +4dBu?
Another point of great confusion. 0 VU is whatever nominal
operating level is. On "pro" equipment, it's usually +4 dBu.
On "semi-pro" equipment, it's usually -10 dBV. On some phone
company, it's +8 dBm (a unit of power, not voltage, but
usually into 600 ohms, so you can calculate the voltage). On
a consumer tape deck, who the heck knows? Usually somewhere
around -20 dBu.
That's the same translation Paul mentioned: +4dBu = -20 dBFS.
Yup, he's a smart feller.
No one has yet answered the question about whether it's FS sine
or FS square.
It doesn't really matter until you want to find the RMS
value of the waveform that got you to that digital level. If
0dBFS = +24 dBu, either a square wave or a sine wave with
the same peak value will get you there.
The RMS value of a sine wave is 0.707 (1/2 the square root
of 2) times the peak amplitude. The RMS value of a square
wave is the same as the peak amplitude.
--
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