Hi,
Make sure that the 150 ohm resistor is mounted inside a metal
connector with the case on it -- if it is open, you will pick up hum
and interference.
---
In Dan Dugan <> wrote:
> Where there is no analog output, like an MD recorder, I dunno!
You would inject a known tone level into the recorder mic input (say
-40dBu), adjust the record level to just under zero on the meter (so
it doesn't clip), and record it. Stop the recorder, substitute a 150
ohm terminated dummy plug for the signal, and record some noise. Then,
play back the tone, and adjust your playback system for a calibrated
output level. Then when the tone stops, you'll hear the section with
noise.
To measure noise, you'd measure the level difference between the tone
and the noise, and then subtract this from the input level (-40dBu in
this case) to get the EIN. Without measurement instruments, you'd have
to do the same test on different recorders, setting the tone to play
back at the same volume and then compare the noise subjectively.
This tests the total system, which is probably more relevant anyway
for a recorder. Note that you'll get different results when you use
different input signal levels -- obviously more noise with a lower
signal level like -60dBu, but the EIN will change also and the
relative ranking of the recorders could vary.
What signal level is relevant to nature recording? That
complicates things, as the record gain will depend on what you are
recording, and the output level of your microphone. And then, another
factor is to determine the noise level of the microphone, and at what
point that swamps out the recorder's preamp noise.
At some point, I plan to do measurements on a bunch of recorders using
my Audio Precision and write this all up in a paper. I might see what
publications would be interested. So far, there are lots of reviews of
different recorders, but many don't have real hard measurements, or
the measurement methods are different so they can't be compared.
- Adam Liberman
Liberman Sound
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