Why is 15 a reasonable mask-level value in the example Help->Browser...->PureData/->3.audio.examples/->I04.noisegate.pd? Mask-level multiplies the frequency-indexed average noise levels contained in the mask table before they are used as gate thresholds. I'd expect that 1.5 would suffice and that 15 would exaggerate the gain reduction so much that it would leave unintended artifacts, yet that's not what I hear. For values between 0 and 4 I hear mp3-like chiming which goes away above 6. Miller Puckette discusses the algorithm in Theory & Technique of Electronic Music ch 9.4.1, but there's no mention of scaling the threshold function f[k]. The only thing I can think of is that maybe the distribution of noise powers for each frequency over time is so broad that you need a factor > 6 to include most of them?

Update: if I bypass the q8_sqrt~ things behave as I expect them to. I don't understand why he's taking the sqrt anyway--there's no mention of it in the gain equation g[m,k].

Another thing I don't understand is why the gain reduction is calculated in terms of power instead of amplitude. The next two examples, a compressor and a vocoder, both use amplitude. Is there something special about noise gating? I modified the noise gate to use amplitude instead (by moving the sqrt~ up to just after the sum of squares) and it sounds just as good to me.

@jameslo Amplitude does not estimate the peaks between measured spectrum frequencies.......... http://www.ni.com/white-paper/4278/en/#toc4 so with only 511 points in the mask table power should be a better choice.
I cannot get my head wrapped (good pun) around the combination of the block size and up-sampling in relation to [tabreceive~] but you will probably find that it doing what is explained in the above link.
I will post again if I get there...!
If I was trying to achieve the same thing I would have been bogged down in an object that interpolates, but Miller is much better educated than me.

I don't understand why the patch was called "noise gate" though, when it is noise reduction by process.
It seems to do as good (usually bad) a job as the pro daw equivalents that I have.
The multiplier at 15 does a very good job of totally cancelling all of a Pd noise source set to 100 on the generator. I assume the math is correct.
David.