Deaf Cat said the following on 09/09/2005 19:06:
Errrrm, I do feel a little daft joining in this conversation about
attenutation and dB and 0dBu's as I have not got the faintest idea what
you rather technical people are all talking about, but would like to
learn a little if possible...
Good attitude!
The Preamp Volume Control is default Zero, which means full volume.....
approx. 2Vrms? - (normal CD o/p)
The std SB2 output is 6v(peak to peak) which is 3v(peak) or 2.12v(rms).
"Normal" CD output tends to be 0.775v(rms).
I guess attenuation has something to do with adjusting the signal level
which in this case equates to the volume.
Correct. Attenuation means reducing the level.
The range 0.0 to 63.0 - So the setting 0.0 being approx. 2Vrms and 63db
being 0V, if I had a power amp that likes 0.8V, a setting closer to the
63.0 than the 0.0, would please the power amp...?
Not quite. dB (decibels) are a logrithmic measurement, usually
referenced to some standard value. dBu are referenced to 0.7746v.
For the stock SB2, output is 2.12v(rms). In dBu, this is:
20 x log10(2.12 / 0.7746) = 8.75dBu
Say you want to reduce your output to 0dBu, you need to add 8.75dBu of
attenuation. This would reduce the max Vout(rms) to 0.7746v.
So, the firmware lets SB2 know what these settings mean, or does the
firmware help with SNR?
The firmware is the bit that implements this functionality by
controlling the DAC chip in the SB2.
If you do understand how I am thinking, and what I would like to
understand in the simplest form, I would love to hear nice simplistic
explanations if possible, thanks for your patience.
I hope the above helps.
BTW, the firmware has just been relased. I've downloaded it and can
report that it's working well.
I'm not sure that the way of setting the attenutation is the most
intuitive of user interfaces, but it does the job.
R.
--
http://robinbowes.com
If a man speaks in a forest,
and his wife's not there,
is he still wrong?
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