User talk:PeterSampson/Sand-Box

Artifacts

You may get tinkly artifacts happen when individual pure tones are near the threshold to be preserved - they are small pieces of the background soundscape that survived the thresholding, perhaps because the background noise is slightly different from the fingerprint or because the main sound has overtones that are imperceptible but that boost them slightly over the threshold.

The Sensitivity slider biases the thresholds of all frequency bands. Higher settings will thus reduce the number of artifacts, but at the risk of introducing the opposite discrimination error, in which parts of the desired signal are misclassified as noise and so reduced. The purpose of the Residue radio button is to pass the difference between the original sound and what would result from choosing Reduce. When the Sensitivity is excessive, "tinkle-bells" will be heard in Residue rather than in Reduce, and where the original had louder sounds, rather than in the pauses between sounds. By previewing the results of Residue before applying the effect, the best Sensitivity balance can be found.

• Paul 24Jan15: I almost want this paragraph in the Manual rather than here. Just remove the talk of "discrimination."
  • Gale 25Jan15: I assume you mean the paragraph above this ednote, Paul? The final paragraph below this note would need a lot more explanation if it was in the Manual. If you mean above, I'll see if I can work it in to the Manual if no-one else does - that page looks somewhat unfinished (still two P1's).

    Can "Residue" still be roughly described as per the Development Manual's current description "the sound that is removed"? "Residue" probably means less to most users than the old (not working properly) "Isolate" did, so I guess few will use it. Should it have been called "Invert" or "Difference"?

  • Paul 27Jan15: I mean the previous paragraph. "Residue" was Steve's preferred term. One might want the difference of wet and dry signals (Residue), or to pass the noisy part of the signal full strength, ignoring the reduction, attack/release, and frequency smoothing (Isolate). Old Noise Removal's buggy Isolate didn't really do either. The alpha version of Noise Reduction made both available. I think "sound that is removed" [be careful not to say "noise"] describes not Isolate but Residue, well enough. Finally the suggestion for mixing below isn't from me. I never tried that. What I have written is still an incremental update of an original that I think was Dominic's.

The Frequency Smoothing slider does not affect the number of artifacts, but it can make each less evident by spreading the effects of discrimination errors among nearby frequency bands.

You can reduce the effect of tinkle bells by noise gating sounds that are well separated (either in volume or frequency spectrum) from the background noise, or by mixing a small amount of the original noisy track back into the noise gated sound. Then the muted background noise tends to mask the tinkle bells. That technique works well for (e.g.) noisy microcassette recordings, where the noise floor might only be 20 dB below the loudest sounds on the tape. You can get about 10dB of noise reduction that way, without excessive tinkly artifacts.