TO Attenuate or NOT to Attenuate

[EJasonC]

WHAT is the recommended method?
TO attenuate or NOT to attenuate?
At FULL volume or FIXED, my source device (DAC) outputs 5.2V.
With attenuation (-6dB) ENABLED, my PRE/PRO's balanced input has a limit of 4.8V or more.
With attenuation BYPASSED, the limit is 2.4V or more.
SHOULD I attenuate OR should I bypass attenuation while adjusting volume of source by -6dB?
I suppose this could be a gain staging scenario?

 

[Vincent Kars]

Your DAC outputs 5.2V. Way to high for your PRE. So you must attenuate at the DAC to bring it closer to the 4.8 of your PRE

The PRE says it is 4.8 V on the XLR with its own attenuator "on". Off it is 2.4. As the DAC output is far in excess of 2.4, you must set the attenuator at the PRE to on.

 

[EJasonC]

Your DAC outputs 5.2V. Way to high for your PRE. So you must attenuate at the DAC to bring it closer to the 4.8 of your PRE

The PRE says it is 4.8 V on the XLR with its own attenuator "on". Off it is 2.4. As the DAC output is far in excess of 2.4, you must set the attenuator at the PRE to on.

Thank you Vincent!

If max volume setting at DAC is +1.5 dB (see pic), I assume +1,5 dB equals 5.2V.

What dB setting equals 4.8V?

 

[danadam]

If max volume setting at DAC is +1.5 dB (see pic), I assume +1,5 dB equals 5.2V.

What dB setting equals 4.8V?

20 log(4.8/5.2) = -0.7 dB, so if +1.5 dB gives 5.2 V, then 1.5 - 0.7 = +0.8 dB will give 4.8 V.

 

[EJasonC]

20 log(4.8/5.2) = -0.7 dB, so if +1.5 dB gives 5.2 V, then 1.5 - 0.7 = +0.8 dB will give 4.8 V.

I'm not sure what 20 log means, but probably doesn't matter because the DAC increments at 0.5 dB intervals. I guess I'm safe at 0.5 dB then. Thank you all for your insights!

 

[DVDdoug]

I'm not sure what 20 log means

20 x Logarithm. You'll find it on a scientific calculator or spreadsheet. That's the formula for amplitude (digital value or voltage). There's a different calculation for power (Watts). It ends-up the same but it's a different calculation. (I've got a dB spreadsheet set-up.)

Decibels are always relative/proportional. In this case we are calculating a dB change.

The reference for acoustic loudness is 0dB SPL (sound pressure level) and it's approximately the quietest sound that can be heard. Dead silence in outer space is minus infinity dB.

The reference for digital data is 0dBFS (zero decibels full scale) and with regular integer formats it's the highest you can "count to" with a given number of bits. So digital dB levels are normally negative.

There is no automatic calibration between digital and acoustic levels but there is a direct correlation... If your digital level drops by 3dB (a bigger negative number) the SPL level also goes down by 3dB.