I'm planning on doing some comparative measurements soon (for an
article in the Nature Sounds Society newsletter "Nature Sounds") to
compare mic pre-amp noise between different MiniDisc (and possibly
hard-disk) recorders, both consumer and professional, and with and
without external mic preamps. These measurements will be done on my
Audio Precision System Two Cascade.
(I may be looking soon for local San Francisco Bay Area volunteers
to bring by their recorders and preamps so I can measure a variety
of models).
There has been a lot of discussion but as far as I know no hard
comparitive data in this area. This would answer the questions of 1)
What is the measurable advantage to using an external mic preamp (if
any), 2) Does a particular recorder benefit from an external mic
pre, and 3) What (if any) is the noise penalty using a consumer
(Sony, Sharp) MiniDisc recorder. To be completely valid, these
measurements will need be done on separate components and also
including the entire signal chain -- external mic pre connected to
the recorder in question.
Mic preamp EIN (equivalent input noise) in my experience can vary
some depending on the gain level, and the published specs for music
recording are not done at the high gain levels typical in nature
recording (I'm talking about EIN, not Signal-to-Noise, which
obviously changes with gain).
Mic preamp noise is measured in EIN (equivalent input noise), which
is the increase in noise contributed by the mic preamp over the
theoretical noise level of the source impedance. Most professional
quality mic preamps claim an EIN of 1.0dB or less, which means they
shouldn't contribute any significant noise to the signal, and the
noise heard would come almost entirely from the microphone circuitry
or capsule itself.
This brings up another complication of getting hard data that
translates to real field usage -- the actual source impedance of the
microphone may vary with frequency from the nominal 150 ohm spec, so
measurement of the source impedance of some popular microphones and
the EIN of mic preamps over a range of impedances and frequency
would be in order. Anyone have some mic test heads for various
models (I have one for the Schoepps)?
Any comments?
- Adam Liberman
Liberman Sound
www.libermansound.com
________________________________________________________________________
________________________________________________________________________
|