CLEAN attempts to reduce noise in a signal by eliminating low-level bands that are quieter than those in a comparative 'noise file' (Input 2). The 'noise' signal is a sample of noise (only), normally from the signal file. It could be ambient noise, for example. Mode 2 additionally subtracts noise from bands that have been passed (CDP: specnu subtract). MODES 1. CLEAN: Eliminate frequency bands quieter than than those in the noise file 2. SUBTRACT: Eliminate frequency bands quieter than than those in the noise file and subtract noise from those passed. PARAMETERS persist: Minimum time for which the signal must be greater than the noise level to be retained. Range 0-1000 ms noisegain: Multiply levels in noise file channels before comparison with signal. Range 1 - 40 NOTES Like the original SpecClean function (now in XTRA menu), this uses a second "noise" file for comparison. In the earlier version, bands near the noise threshold were judged to be signal or noise (as appropriate) from one analysis window to another, and this constant switching led to an unwanted "bubble" effect. Here, the persist parameter allows you to decide how long a signal must persist to be retained. Additionally noisegain allows you to boost the noise signal to make it a more effective cleaner. Experimentally, the technique could be used to thin a signal by removing content (in File2) which might be in the original. (This worked well with two steady-state sounds, the signal being a complex chordal sound and the "noise" file being a whirring sound.)
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