On 10/31/2019 8:50 PM, Tobiah wrote:
How would you do it?Â* I have one of those 150 Ohm terminators
that you guys told me how to make.Â* Given two USB audio interfaces,
what would be your procedure for comparing the two units (like
deciding which one to keep) with regard to the mic pre's, mostly
for noise figures.
I'd keep the one you like best for other reasons - included features,
understandable user interface for its internal mixer if it has one,
range of the gain control, convenient input and output connections,
reputation of the company.
Don't worry about measurements. Unless you're doing some recording that
requires very high gain with very low noise - in which case you probably
should be using an outboard mic preamp - preamp noise shouldn't be a
problem. But if you really want to measure something, connect your input
terminator, turn the input gain up all the way, record what's coming
out, and take an eyeball average of the playback level meter when
playing your test recording. You may need to add 30 dB or so of gain to
the "track" before you can read anything.
If you want to compare gains to throw that into your decision, you'll
need a signal generator. There are a number of ways that you can get a
test tone. If you don't have a signal generator, you can make one from a
computer or even a smart phone, by recording a WAV file and playing it
back. Connect your test signal to the mic input of one of the
interfaces, adjust the level of the signal generator so that you get a
record level of around -6 dBFS, then switch over to the other interface
and, with its gain control turned up full, and see if the record level
is higher or lower than the first one. If you find that one has several
more dB of gain than the other and the noise level is very close for
both, that's the "better" one.
But, as Scott said, noise isn't transparency. Listening is the best
measure of that since you're looking for something that's a matter of
personal taste. But you can use the program Room EQ Wizard to measure
harmonic distortion with respect to frequency, and see which harmonics
are predominant over the frequency range. That could give you a clue as
to expected "warmth" or "clarity."
If Recording Magazine would get back to putting some useful technical
stuff into their articles, they might get back to running my apparently
abandoned (with the new editor) Trust But Verify series that explains
how you can test your gear with things you're likely to have laying
around the house, or that don't cost much.
--
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http://mikeriversaudio.wordpress.com