Re: Calculating peak level in db
Re: Calculating peak level in db
- Subject: Re: Calculating peak level in db
- From: Gerd Castan <email@hidden>
- Date: Sat, 12 Oct 2002 23:45:01 +0200
Brian,
Gerd Castan <email@hidden> asked:
[ in an simple test input, my M-Audio Delta Control Panel shows a
[ peak level of about -12 db
[
[ The peak sample values that my audio recording application sees
[ is about 0.1 which is about e^{-2} which I display as -2 db.
[
[ Where is my mistake that explains the difference of 10 db between
[ the control panel and the values I get? I don't set any values
[ like gain in my application.
In general, dB is a relative measurement, not absolute. For PCM, the
convention is to consider full scale as 0 dB. For signals in the analog
domain, such as those flowing down balanced or unbalanced cables, there are
standard voltages which are used as a reference. These do not necessarily
correspond to full-scale PCM, because each A/D circuit can be designed with a
different power supply reference, and therefore the same analog voltage might
convert to a different digital value with different circuit designs.
In the analog world there are several dB scale references like dBm, dBmV,
dBuV, etc. Each has a specific voltage defined for 0 dB. Search for these
unit abbreviation on google. Also, professional balanced gear is usually +4
dB, and unbalanced is at -12 dB. I forget which scale is used for measuring +4
db and -12 db (it may be referenced to 1 V peak-to-peak or maybe 2 V), but I
imagine that you had unbalanced (phono) cables plugged in with a signal at a
standard level, which is why the panel showed -12 dB.
Just remember, it's all relative...
Does this mean my assuption is wrong, that the maximum sample value I
can get is 1.0?
And if it's wrong, which is the maximum sample valus I might get?
Thanks,
Gerd
Brian Willoughby
Sound Consulting
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