On 3/8/2019 4:10 PM, Tobiah wrote:
When recording quieter things
as I've described, I need to turn the gain up all the way (they
say it's 60dB) and I then hear loads of whiteish noise. What's that
trick I can use to make sure it's not coming from the mics or room?
A resistor placed correctly?
Make a "dummy mic" by connecting a 150 ohm resistor between pins 2 and 3
of an XLR plug. Plug it into the interface, turn the gain up full, and
record the noise. You don't actually need to record, just read the
record level on the meter of your DAW program.
The unit sometimes generates odd blips and squeals which had me
looking at replacing it. It's also really old and was not supported
past Windows 7. I'm running 10 right now.
Most audio hardware that runs on Windows 7 will work OK on Windows 10,
but it is rather old and the PreSonus probably has better converters in
it. That in itself won't make it any quieter, but it'll probably have
lower distortion than your old interface.
The Presonus 1810 looks
like it does everything I'm used to. I know this means nothing
scientifically, but since they rate their preamps as providing
80dB of gain, I thought, hey, maybe they'll at least be quieter
than the ones I have at 60dB.
It doesn't really have 80 dB of gain. What the spec sheet says is that
it has 80 dB of gain RANGE. This is significant at the opposite end of
the scale than what you're concerned with. It means that if you have a
sensitive mic on a loud source, you can reduce the mic's output level
going into the preamp by as much as 80 dB so that it won't clip. In
reality, it means that you have about 20 dB of attenuation available to
handle loud sources.
Unless you get inside the box and measure the output of the preamp
directly, you really don't know how much gain it has. Since there's no
standard relationship between the input level (volts or dBu) of the D/A
converter and the digital output level (dBFS - what your DAW meters
read), you can't work backwards from the DAW meters to get the preamp
gain. Gain is volts out divided by volts in, not bits out divided by
volts in.
If you have a signal generator and a way to measure its output voltage,
you can measure how many millivolts (or dBu) it takes to give you 0 dBFS
out. This is a spec that's rarely published for an interface like this,
probably because the manufacturers know that most users wouldn't
understand it. If I'm writing a review, I'll measure it and put it in
the review for those who care.
When you know the sensitivity of the preamp and converter combination,
by using the sensitivity of the mic, which is a commonly published spec,
if you know how loud your source is (in dB SPL) you can calculate what
level that will give you going into the preamp. The NT-1A Sensitivity is
-31.9dB re 1 Volt/Pascal (25.00mV @ 94 dB SPL) +/- 2 dB @ 1kHz.
The good thing about the NT-1A is that is has quite low noise output
with no signal (5 dBA SPL equivalent), so the mic itself doesn't
contribute very much to the noise that the A/D converter is going to
convert to digital signal.
By the way, I don't know if this carries through the full Studio line of
PreSonus interfaces, but there's something odd with the output metering.
A friend of mine got a Studio 192 (I think that's it) to use to digitize
some tapes. He noticed, when setting the input gain from the alignment
tones on the tape, that at low frequencies, even though the level of the
tone was steady, the meters would slowly move up and down. The digital
recording was fine, it's just the meters on the output were going
bananas. I suspect that it was aliasing in the LED driver. PreSonus
never noticed it, had no idea what was causing it, and didn't care since
it didn't affect the recording.
You can watch the video he
https://www.youtube.com/watch?v=AHHG9lzQYxc
The two meters that are steady are the input level, the two that bounce
are the on the interface output (which is also steady).
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