I/O Matching: Mic Pre and the Converter

Archived from groups: rec.audio.pro (More info?)

Hello!

I'm trying to understand the relationship between mic pre's and A/D
converters as far as the Mic Pre's Max Output and the Max A/D Input is
concerned.

Most manufacturers of dedicated Mic Pre's (Great River, Hardy,
Millennia, True Systems, Manley, etc) produce units with differing
maximum outputs: you get everything from +24dBu (60 Ohm) to +32dBu
(24.3 Ohm).

Same variation exists with maximum input on A/D converters: examples -
Lavry Blue +24, Lynx +20, MOTU 192 +18, etc.

How important (in terms of sonic quality - of course!) is it for these
to match? It seems to me that you would want your mic pre and
converters to be as close as possible - so as to maximize dynamic
range, for one. (However, it's been my experience that 'common sense'
when dealing with technical issues is usually wrong!)

Should this 'matching' be a consideration at all when purchasing a
pre-amp? Or is this a non-issue - simply a matter of turning down the
output on the preamp so that it doesn't exceed the input of the A/D
converter? From a technical standpoint, are there any potential
reductions in sonic quality by limiting/reducing the voltage of the
preamp output?

(Again, seems to me there would be. In my experience, S/N is better as
you ride wide open, for example.)

Thank you for your patience with my questions. Of course, the actual
sound of the preamp is the overriding value for me, but I would like
to better appreciate the technical aspects.

Harry

Archived from groups: rec.audio.pro (More info?)

"Harry Houdini" <harry@home.com> wrote in message
news:htb3i15g5r2hjo53pk462galvsmbrder53@4ax.com
> Hello!
>
> I'm trying to understand the relationship between mic
> pre's and A/D converters as far as the Mic Pre's Max
> Output and the Max A/D Input is concerned.
>
> Most manufacturers of dedicated Mic Pre's (Great River,
> Hardy, Millennia, True Systems, Manley, etc) produce
> units with differing maximum outputs: you get everything
> from +24dBu (60 Ohm) to +32dBu (24.3 Ohm).
>
> Same variation exists with maximum input on A/D
> converters: examples - Lavry Blue +24, Lynx +20, MOTU 192
> +18, etc.
>
> How important (in terms of sonic quality - of course!) is
> it for these to match? It seems to me that you would want
> your mic pre and converters to be as close as possible -
> so as to maximize dynamic range, for one. (However, it's
> been my experience that 'common sense' when dealing with
> technical issues is usually wrong!)

You've got to consider the whole system which is sound
source, mic, mic preamp and converter.

Only the output of the converter is in any sense globally
standardized, that is cast in cement. Digital FS is a
diamond-hard wall.

Mic preamps have gain controls with an incredible range,
usually 50 dB or more, for a reason. To make all of the
above as compatible as possible.

The reason that people prize good converters and good mic
pres is to make matching as non-critical as possible.

> Should this 'matching' be a consideration at all when
> purchasing a pre-amp? Or is this a non-issue - simply a
> matter of turning down the output on the preamp so that
> it doesn't exceed the input of the A/D converter?

The latter.

> From a
> technical standpoint, are there any potential reductions
> in sonic quality by limiting/reducing the voltage of the
> preamp output?

I'm sure you know that:

If you run the gain of your preamp too high stuff starts
clipping this sounds very nasty.

If you run the gain of your preamp too low, you start
picking up excess noise. This is more tolerable.

The better the converter, the better the mic preamp, the
wider and deeper the sweet spot.

With converters and preamps in the price range you're
talking, you deserve a deep, wide sweet spot.