PanieriLorenzo
commented
3 years ago A few notes on this update:
- compression effect moved to next release (0.3)
- new "dropout" effect planned for next release (0.3). Dropout works in a similar way as flutter, but is performed as gain reduction rather than time shifting
- make playback hiss entirely de-correlated as quantum already adds a lot of correlated noise
- add recording hiss before all the effects except for pre-gain, in essence there are three places noise is introduced in real life: the noise floor inherent in the recorded signal, the noise added by the tape grain (quantum) and the noise inherent in the playback circuit
- consider adding cross-talk between left and right channels after hysteresis but before saturation, this effects is extremely subtle on real tape, but maybe it's worth adding.
Closing statement: it would be nice to have a super rudimentary version of OpenDSPL working to facilitate development (writing difference equations in rust is a pain, as rust really likes to not have side-effects) Or maybe work Faust DSP into the workflow, to generate difference equations which can be pasted in rust.
New signal path, all distortion algorithms re-designed.
All items without "see below" are taken from existing code and are not explained here.
Hysteresis (redesign)
Real hysteresis happens because magnetic particles need a minimum threshold to be moved. Thus the new implementation simply introduces a crossover distortion on the derivative of the input, which is then re-integrated to generate the distorted signal. This is simply what used to be the crossover from the original implementation.
Saturation (redesign)
Saturation algorithms are similar to the existing ones, but less over-engineered. Here
xis the absolute value of the input, which is then multiplied with the sign of the input to restore the original polarity.(x*x*x*1.6 + x*0.4).tanh()(x*x*x*3.0 + x*0.75).atan()*2.0/PI(x*1.6).atan()*2.0/PIx.tanh()(3.0*x.powf(1.8)).atan()*2.0/PIVoltage-drop compression
Drive is increased (without increasing anti-drive) dynamically after the attack time has past. In essence creating compression. This effect slowly comes in only if the input is loud enough, following a tanh compression curve. Attack and release are set by the user. This is because in real tape, if the tape is saturated and kept saturated for a sustained amount of time, the tape cannot absorb any more energy and the saturation threshold lowers. This let's transients through with little distortion, but sustained sounds are distorted more.
Wow-flutter
Wow is introduced with two lfo's added together. LFO 1 ranges 0.5 Hz to 2.5 Hz. LFO 2 ranges 1.0 Hz to 3.0 Hz. The two are controlled by a third triangle LFO so that when one is at 0.5 Hz, the other is at 3.0Hz, and vice versa. The two are added together creating a somewhat unpredictable oscillation. Flutter is introduced by modulating with filtered noise. The noise is bandpassed by the following filter: Feedback coefficients:
[-2.0, 1.0], feed-forward coefficients:[0.012, 0, -0.012].Self-erasure
Self erasure of treble content happens through soft-clipping of the derivative of the input.
Playback hiss
Playback hiss is introduced by amplitude modulating pink noise with a small DC constant summed with the input itself.
Tube plugin proposal for the future
The tube functinality should be moved to a new plugin. A few features: