If you don't believe me, do this simple test:

feed a 1kHz tone in to the input

set 'analog volume' control in software to 0dB

connect to ardour or your choice of recorder with decent metering.  set meter point to 'in'

increase volume of test signal until you are getting 0dBFS.  no matter how much you increase the level of the test signal from here it will continue to read 0dbFS.  turn the signal generator up a good few dB so you are well in to clipping.

record a bit of this.  you will see a squared off wave.

now turn down the 'analog volume' control until you are seeing a nice comfortable level.  do not change the level of the test signal generator.

record again.

the result will still be clipped.

in fact it will be identical to the first signal you recorded, just scaled down.

I mean, you guys do whatever you want, but that is what is actually happening in your signal chain.




On Sun, Jul 17, 2016 at 10:45 PM, Len Ovens <len@ovenwerks.net> wrote:
On Sun, 17 Jul 2016, Tim E. Real wrote:

On Saturday, July 16, 2016 11:17:10 AM EDT Robert Edge wrote:
There is no actual analog volume control on the 1010LT's RCA inputs, it's
just doing multiplication on the captured signal after the ADC.

What -  did I read that right?
This card definitely has analog volume input control.
The 'Analog Volume' mixer tabs in Envy24 or Mudita24 control it.

 Not having one, it is hard to be sure. I am pretty sure that the analog levels are sent to the ADC chip and are not done on the ice1712 itself. I know that the LT uses a cheaper ADC than the D66 which uses a cheaper chip than the D1010. Possibly the ADC itself does digital volume control, though this is not something I have seen in any of the chips I have looked at (not that I have looked at a lot).

The more likely thing is that the clipping is happening in the analog ciruitry before the ADC. All of these cards take their voltages from PCI (+/- 12v - ish) That has to be dropped a bit to get anything like DC voltages through regulation. A +4 input does not peak at +4 but might peak as high as +27dBu (for the MPAII in question) which is about 50 v p-p... I would call that clipped with no pad in front of the gain stage.

Note that the audible clipped peaks would generally not show on a dBu meter like that on the front of the MPAII.

This why the LT has jumpers for the balanced inputs. So that the input level can be dropped to within the that +/- 12v range that the gain stage has to work with while still being able to be used as a mic input... using passive padding before the active stages get to it.

--
Len Ovens
www.ovenwerks.net


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