[LAU] [Music] Sans titre - Without title

Len Ovens len at ovenwerks.net
Mon Jul 18 02:45:47 UTC 2016

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

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