Re: M-Audio DMP-3, Is It Quiet?? Transparent??

"David Satz" <DSatz@xxxxxxx> wrote in message
news:1177295217.284168.186410@xxxxxxxxxxxxxxxxxxxxxxxxxxx

One of the preamps (DMP-3) had a roll-of below 80 Hz and
a really sharp roll-off below about 55 Hz.

That's not true of my DMP3 here. It isn't perfectly flat,
but it's only 0.1 dB down at 50 Hz relative to 1 kHz, and
only about 0.3 dB down at 30 Hz. Signal levels = -24 dBU
in, HI/LO gain switch is set to LO, gain knob set so that
the front panel meter read 0 dB at 1 kHz. I'm running
these signals right now as I'm typing.

Perhaps the misunderstanding occurred because the
preamp's front panel meters roll off at low frequencies.
They certainly aren't precision instruments.

My comments about frequency response were based on comparisons related to
musical signals that had passed through other preamps. Either they had some
massive low-frequency boost, or the DMP0-3 was rolling off. I'm not familiar
with it at all, so I don't know if there is a switchable low-frequency
filter, or if its performance varies with settings of the hi/lo switch.

--I did a series of fairly careful preamp noise tests
including an RNP and a DMP3 a couple of months ago, as
well as other preamps (a Millennia Media HV-3B, a Grace
Lunatec V3, a Symetrix SX202, a Sonosax SX-M2, a dbx 760X
modified by Jim Williams and a Telefunken V 72 restored
by Oliver Archut). The DMP3 came out rather differently
depending on the setting of its HI/LO gain switch, since
I was testing at the same gain either way (around 40 dB),
and this forced the gain knob to be set rather low in the
HI position of the switch and rather high in the LO
position.

I guess this means that the hi/lo switch doesn't change the LF frequency
response very much, if at all.

The DMP3 with its gain button in the LO position did
extremely well in these tests--within 1/4 dB of the
Millennia Media preamp. By the way, the RNP was within 1
- 2 dB of that figure as well. I don't want to post any
absolute measurement results since they depend so greatly
on how the noise spectra are weighted, on the gains
chosen, and on the associated equipment.

But just by way of explanation, the input to the preamps
wasn't a short or a resistor pair, but an actual
condenser microphone with a measurement test head in
place of its capsule, with phantom powering applied so
that a realistic amount and kind of input noise would be
present as in a real recording with that type of
microphone. The gain at which I measured all the preamps
was typical of the gain I need for classical concert
recording.

Presumably with minimal micing?

One thing which I found early on is that with "mere"
16-bit recording, it was nearly impossible to detect any
differences among preamp noise levels at all--I had to
switch over to 24-bit. That alone implies something about
preamp noise: There's a real chance that some people may
be overly concerned about it, at least some of the time.

Agreed. I don't have a mic with a measurement head, but I do know that with
phantom removed, the noise floor of my recording setups drops another 10-20
dB, depending. I take that to mean that the room and the mic itself are the
dominant sources of noise.


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