Confusing and technical, working out how much hiss is going to come out of your recording down to the bits you use is important. And difficult to understand.

I have a few microphones and combined with different recorders, don’t sound consistent. Issues being all the elements that make up the chain between the noise itself and the recorded sound. That’s going to include the noise source, background noise (that the brain often filters out), the microphone, the microphone cable, the recorder and any compression artefacts added to the recording if you are not using an uncompressed file format.

I have also been trying to unravel the technical details to understand why. So I used a little bit of Google and quite a bit of reading. In the end I didn’t really get to grips with it, so I will carry on knowing how my gear works in which situations (which is probably the best approach). Here are a couple of snippets of interesting details/science/etc.

I found this as a good start point, a rule of thumb for microphones.

Max SPL = The point where the mic distorts, or clips the waveform. [More=better]
Self noise = The amount of noise the mic creates all on it’s own. (i.e. hiss). [Less=better]
Dynamic range = The range between self noise and Max SPL. [More=better]
Signal to Noise ratio = The range between self noise and a reference signal. [More=better]

Reference

So a good start.

But then you don’t always get this data from all microphone specifications. So this explains on how to fill in the gaps.

Some mics may only provide a specification for signal to noise ratio instead of self-noise. Higher numbers are better on this one. Fortunately you can figure out the self-noise from this if they provide enough info. Typically microphone signal to noise ratio is related to a reference acoustic level of 1 Pascal (Pascal is a unit of pressure and relates to “Sound Pressure” [SPL]). A typical rating might be 70 dB, 1 Pa @ 1 kHz. 1 Pascal is equivalent to 94 dB SPL. So, for a S/N ratio of 70 dB you can assume the self-noise to be 24 dB. There are a variety of testing methods, standard, and units of measurement that can come in to play to further muddy the waters, but you will find that most reputable microphone manufacturers will generally give you enough information in a standard enough format to make a comparison.

Reference

So what does this mean then? For nature recording, getting close to the subject with any thing will give a good result. Further away from the subject will require more recording gain, therefore potentially more recording hiss.

What I usually do is record at relatively low levels quieter sounds and then use an audio file editor (usually Audacity) to amplify. when I can hear hiss being introduced I usually then filter out with a low pass filter. If the recording is used on its own you can hear the difference, but if mixed in with something else, rarely heard.

For mechanical sounds, things are a bit easier. High pass and low pass filters can be used to cut our unwanted sound and also enhance wanted sound. Using a spectrum analyser is sometimes useful for finding out these frequencies. Additionally to high/low pass filtering, EQ can be used to address specific noises on specific frequency bands.

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