On 3/18/2019 7:50 PM, Tobiah wrote:
I ordered a Jethead Phantom to see whether it would improve
the S/N used with my NT1-A's, and an M-Audio Fast Track
Ultra audio interface.Â* I also have a 'dummy mic' as we
recently discussed, using the 150 Ohm resister soldered into
a male XLR connecter trick.
Given the dummy mic, the microphones, the interface, and
the Jethead which will arrive on Wednesday, how would you
go about deciding whether the Jethead is going to be able
to deliver clean enough gain that it surpasses and improves
my existing preamps.
Your first though was correct. Just listen.
If I wanted to measure what it was doing (and indeed I'd do this if I
was writing a review of the product), I'd do something similar to what
Paul suggested.
First, connect the mic that you intend to use to the interface you
intend to use, and set the input gain on the interface so that you get a
good recording level. Do this in a quiet room, maybe waiting until late
at night to reduce stray noise.
Replace the mic with your dummy, and make a quantitative measurement of
the noise level. If you'd like to be more "classroom" about it, replace
the mic with a signal generator and adjust the generator output (not the
interface's preamp gain) to give you a steady tone at that level, and
then replace the generator with your dummy mic. Although you'll need to
make up a cable for it, I find that the function generator phone app
from Keuwlsoft works quite well.
Put your DAW program into the Record mode on a track and read the
meters. They may be below -80 dBFS, so if your program gives you the
option of setting the minimum level on the scale, do that accordingly.
The meters will be bouncing around, so take an eyeball average and write
it down. A more instructive procedure would be to use a spectrum
analyzer to see if there's anything there besides random noise - hum,
for instance. I like the DAW plug-in SPAN from Voxengo, but some DAW
programs have a spectrum analyzer built in, though, like Audacity's, the
scale is limited to reasonable music levels and won't show a small
amount of noise.
After you have a reference reading of the noise level without the
pre-preamp, put it in line ahead of the interface and again, adjust the
input gain on the interface to get back to your reference level - either
with a mic or a signal generator.
Now, plug your dummy mic back in and look at the noise level. If the
pre-preamp claims to have 25 dB of gain (and you can confirm that with
the same test setup) you won't find an improvement of 25 dB in
signal-to-noise ratio, but you should find some improvement. Don't be
surprised if it's less than 10 dB - molecules are going to move no
matter how good the specs look.
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