> For example, if your H4n has an EIN of -107 (at full gain), and
> adding your preamp to the chain allows you to reduce the gain on the
> H4n by 35 dB, does that mean the EIN of the H4n has now been reduced
> to -142 dB? I'm really not sure I am understanding this correctly!
John,
No. The Equivalent Input Noise takes any gain setting into account.
Another way to define EIN is the input level which would increase the
audible noise by 3 dB (twice the energy level)
The measured EIN should stay constant whatever the gain settings, but
if not, the lowest EIN should be that measured at high gain. If EIN
goes up with gain, there is extra noise in the recorder. This sounds
odd but you subtract the gain, so the EIN should stay the same.
Another way of looking at this is putting a 10dB attenuator on the
input. The noise level will be the same, but relative to the overall
gain the EIN will be 10dB higher.
The EIN of a line input could be quite high, but that would normally
be swamped by the higher input level going into the line input. What
the Telinga preamp does with PIP inputs is to swamp any recorder EIN
which can be quite high with "affordable" recorders.
What makes EIN difficult to pin down is different noise frequency
profiles, for instance adding LF noise to HF noise. That is why
weighting is used to make measurementrs more standard.
Hope this helps.
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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