naturerecordists
[Top] [All Lists]

MT2496 pre noise masks mic noise

Subject: MT2496 pre noise masks mic noise
From: Gianni Pavan <>
Date: Tue, 18 Oct 2005 21:28:01 +0200
Hi all,
        I tried to figure out how different mics could behave with the
MT2496 and the Mic2496 while recording in a quiet environment. My
target was to understand more of the relationships among sensitivity,
self noise and mic preamplifier noise.

Here the equipment I used:

MAUDIO MT2496 --> 2GBCF
CoreSound Mic2496 --SPDIF--> MAUDIO MT2496 --> 2GB CF
CoreSound Mic2496 --TosLink--> CoreSound PDAudio CF --> iPaq 3870 --> 2GB C=
F
MOTU Traveler --> FireWire --> Laptop

Microphones:

SONY ECM957 (stereo)
AKG SE300+CK98 (short shotgun)
AKG 451EB+CK8 (short shotgun bought 15 years ago)
Sennheiser K6+ME66 (short shotgun bought 10 years ago)
Rode NT1A
Telinga EM23

I used 96K and 24 bits; due to time constraints I did not test all
combinations and permutations; after few tests I focused on comparing
the Rode NT1 / EM23 / AKG SE300 and the MT2496 vs the Mic2496.

I worked in a very quiet room at night. A piezo beeper at 3m distance
in front of the mics was recorded to roughly calibrate levels in post
processing (it makes "bips" and not noise). The Mic2496 was set for
max gain to get the "bips" at about -15 dB with the loudest mics; the
MT2496 was set to High gain position and Max level position (I
avoided to use the digital boost available in the menu' Settings).


The most interesting results I got are that the Mic2496 offers
greater gain and less noise than the MT2496.
By recording with the Rode I got 16 dB more on the "bips" and 8 dB
less noise with the Mic2496 than with the MT2496.
I got the same numbers by recording with the AKG SE300+CK98 (same
sensitivity as the Rode).

It is now interesting to look at the numbers with a different perspective:

The MT2496 noise masks the noise differences of all the mics I
tested!! A Rode NT1, the quietest mic, appears as noisy as the AKG
SE300 and the SONY MS957, that are the noisiest mic!

Thus, to evaluate the real mics noise I used the Mic2496 digitally
connected to the PDAudio system based on an old iPaq (the MT2496
could be used for digital recording as well) or the MOTU.
After adjusting the "bips" levels in post processing (normalization)
I can compile the following list of microphones ordered according to
their noise floor (electronic hiss, above 1 kHz), or, to be more
correct, to the Signal to Noise ratio they can offer if connected to
a quiet preamplifier (I don't consider here the directional
characteristics nor the tonal quality nor frequency response):

Rode NT1 (the quietest)
Telinga EM23
Sennheiser K6+ME66
AKG 451EB+CK8
AKG SE300+CK98
SONY MS957

The disappointing result here is that the AKG SE300+CK98 has a noise
floor 15-16 dB higher than the Rode NT1A noise floor (they have the
same sensitivity and thus the noise floor comparison has not been
affected by the normalization) but its noise was completely masked by
the MT2496 noise and low gain.

The EM23 is 4-5dB more sensitive than the Rode but after
normalization it is 7-8dB noisier.
The least sensitive microphone is the SONY MS957: 15dB less than the
Rode; after normalization it is 17-18dB noisier than the Rode and
only 2-3 dB noisier than the AKG SE300. In the SONY the R channel is
noisier than the L; the L is flat but the R increases at high
frequency up to 6dB more.

These results are the combination of self-noise and sensitivity on a
specific preamplifier whose noise floor is lower than the self-noise
of the microphones, but of course the quietest microphone could have
been affected in some way by the preamplifier noise. Also, the least
sensitive microphones (the SONY) could have been affected by the
preamplifier noise pumped up in the post-processing amplification.

The results on the Rode and AKG have been also confirmed by
connecting them to the MOTU Traveler: the Rode noise was 15 dB lower
the AKG, but the test was disturbed by the fan of the laptop.

The comparison among the Mic2496 and the MOTU is interesting too, but
not definitive because of the fan of the laptop.
The MOTU was set to 48dB gain for both the Rode and the AKG. By
comparing the Rode recording, the bips were 12 dB higher on the MOTU
than on the Mic2496, and the noise was 6-7dB higher on the MOTU than
on the Mic2496. Thus the MOTU allowed a Signal to Noise Ratio 5-6dB
better than the Mic2496.

I hope these preliminary information are useful to understand a bit
more how different combinations of hardware behave and may fit
different requirements.

Sooner or later I hope to be able to repeat the tests with more
accuracy and more devices to compare,
Gianni
--------------------------------------------------------------
Gianni Pavan
Email 
Centro Interdisciplinare di Bioacustica e Ricerche Ambientali
Universita' degli Studi di Pavia
Via Taramelli 24, 27100 PAVIA, ITALIA
Tel        +39-0382-987874
Fax        +39-02-700-32921
Web       http://www.unipv.it/cibra


--
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.344 / Virus Database: 267.12.2/140 - Release Date: 18/10/2005




________________________________________________________________________
________________________________________________________________________

<Prev in Thread] Current Thread [Next in Thread>
Admin

The University of NSW School of Computer and Engineering takes no responsibility for the contents of this archive. It is purely a compilation of material sent by many people to the naturerecordists mailing list. It has not been checked for accuracy nor its content verified in any way. If you wish to get material removed from the archive or have other queries about the archive e-mail Andrew Taylor at this address: andrewt@cse.unsw.EDU.AU