> > The manual of the TASCAM DR-680 for instance shows it's block diagram at
> > page 55:
> >
> > http://www.avisoft.com/DR-680.pdf
>
> It's excellent that they use a separate amp for the line input, instead of
> padding the signal down to go through the mic preamp as many machines do. Not
> so good to have the limiter after the A/D; it won't prevent clipping the A/D.
Dan,
Yes, I guess that they moved the limiter behind the A/D in order to reduce the
manufacturing costs. Everything that is implemented after the A/D can be done
in the DSP firmware, which means that it does not affect the hardware costs.
They might also argue that an analog limiter is seldom required nowadays
because the dynamic range of the A/D converters is sufficiently large for
covering the majority of recording situations.
Bye the way, I just did another simple test on the Olympus LS 5 (whose preamps
are identical to the LS 10/11) in order to find out where the recording level
wheel potentiometer is located in the analog signal path:
I simply set the recording level wheel the zero position and then recorded the
"silence" at both the HIGH and LOW SENSE settings (at 24 bit resolution).
Everyone can do this thest on his or her own recorder without any addition test
equipment.
As expected, the resulting noise floor changed between the two gain settings
(the HIGH SENSE noise level is 16 dB higher than the LOW SENSE noise level).
What does that mean? It just means that the recording level potentiometer is
not located after the last preamp stage, but somewhere in the middle. So, even
if the potentiometer is closed (level 0), we still record the input noise (EIN)
of the last preamplifier stage.
This is indeed a bit different from other recorders and it explains pretty nice
why we have those different EIN values between the SENSE HIGH / level 2 and
SENSE LOW / level 10 settings.
Regards,
Raimund
"While a picture is worth a thousand words, a
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.
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