Thanks for the clear explanation Walter!
Number-wise, my simplistic understanding is that mics capable of
excellent transparency (especially in low sound level environments
where high-gain is common) will almost always possess sensitivity
ratings higher than their self noise ratings. For example, the
Sennhesier MKH-20 has 10 dB Equivalent Noise Level (A-weighted) with
a Sensitivity of 25 mV/Pa+/- 1dB. The AKG 414 is 14/12-- only 4dB
more inherent noise but ~13dB less output. The difference in
transparency in field recordings made with the two mics is dramatic.
Walter, know how sensitivity is measured? Something to do with the
gain required to achieve a certain output,..?
Rob D.
= = = = =
>"Brian M. Godfrey" wrote:
>>
>> This will probably seem obvious once I know the answer: what is good self
>> noise, lower numbers or higher numbers? I was reading about this Marshal
>> MXL2001 and one review said that 20db was kind of high self-noise. I
>> noticed that AudioTechnica has a similar mic for the same price and its
>> self-noise is 12db. I had actually considered using that one in another
>> parabolic that I'm thinking of building, but I'd like to know what to expect
>> of it before I buy. I bought a Samson Mixpad (4, I think it is) and it
>> really introduces a lot of self-noise (if that same phrase can be used in a
>> mixer) into the recording. It's not a problem in surf recording, but you
>> can really hear it when recording birds. Obviously, self-noise isn't the
>> only thing to consider, but it's something that's effected me and that I
>> want to understand.
>> Thanks,
>
>Normally self noise is reported in dB. Two different tests are often
>used, which report in different dB scales, so make sure you are
>comparing the same scale. I usually pay most attention to the dBA level
>reported as that more closely resembles how we hear sound.
>
>They put a mic in a soundproof chamber, with a sound level in the
>chamber of 94dB, set a level meter on it's signal to O dB by adjusting
>gain in the testing equipment. then turn the sound off and read the
>self-noise off the meter. It will, therefore be reported as a negative
>number, and the smaller the number the quieter it is.
>
>Btw, signal to noise ratio is the same test. They just report the
>difference by adding the sound floor value (remember it's negative) to
>the original test sound level. The only other fly in the ointment is not
>all manufacturers use 94dB as their test level, though most do.
>
>Note that this is all at a particular gain setting. As you raise or
>lower the gain, the apparent and metered sound level for the self noise
>is also raised or lowered. So even the quietest mic, if amplified enough
>will have a audible self noise.
>
>The other thing to consider in self-noise (also often called sound
>floor) is what sort of noise it is. Some mics it's a smooth hiss, others
>sputter, crackle and so on. Obviously a smooth self-noise is going to be
>less noticeable.
>
>The Marshal MXL2001 is really designed to be a studio mic or at least
>indoors and is considered a excellent mic for it's price, as good as
>much more expensive mics, with excellent sound characteristics. If
>recording music, which is usually not all that quiet then noise floor is
>not as important. But, we are frequently trying to up the gain to get
>some quiet sound. If you listened to the little clip I did on the
>Marshall's, the noise floor was not noticeable there because of other
>noises in the environment, but I've found them to be a little quieter
>than the specs would seem to make them. As far as noise floor, they are
>usable for nature recording. The more impressive thing about the
>Marshall to me was how far out it was reaching picking up those calls.
>This may be a function of the larger diaphragm, and is part of why I'm
>playing with them. To me the sound is a little richer and the low
>frequency sound better defined than with smaller diaphragm mics.
>
>There are a number of large diaphragm studio mics. I just happened upon
>a good deal for the Marshalls and had read a number of favorable
>reviews. I'm sure some of the others would work as well. To my mind the
>issues that are unknown with this class of mic or any particular model
>is just how well they will handle the environmental conditions we record
>under. That's probably going to be mic by mic in variation. It's really
>a experimental area and it pays to read the various reviews, even though
>they are unlikely to be talking about nature recording.
>
>Yes, you can speak of a self noise for each piece of equipment, it's not
>limited to mics. This is what we talk about when speaking of a low noise
>preamp for instance.
>
>Note with the mixpad, you have to distinguish between the noise floor
>and using it to increase gain and thereby revealing a quieter noise
>floor. I have no idea which it is, have not listened to one of those.
>
>You never eliminate the noise floor, it's just something you are aware
>of and live with. It, more than anything else determines just how much
>you can amplify things. Ideally at each stage through your system you
>want to be well away from both the noise floor and the clipping level.
>And each piece of equipment will have a "sweet spot" somewhere in
>between where it makes the nicest reproduction. Finding those is part of
>learning how to get the most out of the equipment.
>
>Walt
>
>
>
>To unsubscribe from this group, send an email to:
>
>
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
________________________________________________________________________
________________________________________________________________________
|