Re: [LAD] Fader mapping - was - Ardour MIDI tracer

On Thu, 21 Aug 2014, Fons Adriaensen wrote: Really, the whole discusion on fader mapping is very useful and what I say here is based on all of it. I chose this message because it has all the ideas grouped together. The last point first: "The only function of the encoding is to represent the fader position in the best possible way." This should be taken as the starting point. So I am looking at a complex mapping in any case for best use. It appears this: "On the sender side you transmit 0..127 which is just 7 bits of an ADC measuring the voltage from a linear fader or pot, there is no mapping at all." Is not true... or at least not usable as we would end up with some areas of our fade with giant steps from controler tick to controler tick. It seems that for proper information transfer we need .5db per step for 50 to 60 db travel no matter how it is mapped. So there are a number of separate issues: fader position to db mapping db to midi mapping midi mapping to a gain value Fader mapping to db: this requires a physical control with a greater resolution than the midi signal to make mapping possible, or something not quite linear where the physical taper does the mapping for us. db to midi mapping: This depends on the use. On the receiving end is SW that I have no control over and will have to feed what it wants. The least amount of work is to feed it something it knows already. Seeing as my project (this first one anyway) is likely to run inside the same computer as the DAW, it does not make any sense to use an intermediate coding, but rather to mape directly from physical control to the mapping the DAW expects. In the end, the physical controler I have has limited ability to send info to the computer (no analog input) and I will be using rotary encoders. I will not have high resolution input and so I need to map ticks directly to db. Rather than have two different log based sections, I will have one. Based on the software I am controling (Ardour), I will have .5db from +6 to about -40 (though I may go a lot farther as my input is continuous). The output will be mapped to 10bit linear for MIDI and the DAW will add it's own mapping to that. I will do the mapping on my end to match. A full fade will be more than one full turn. I think this is ok because the rotary aspect already makes manual fading unlikely. Because there are no markings on the controler, the mixing point for any channel will always have the same feel even if is 40db down or 3 db up. Because my output has 1024 possible ticks, it will be possible to have a "modifier" button for finer control (or coarser), however, the resolution the fine control can provide will not be in DB but to the limit of the transport protocol which varies over travel. An unmodified movement after a fine one will of course jump to the nearest 127value. For my next project, I will use motor faders and analog input to allow better position to level mapping. In the end, the control board in the controler is the smallest cost, so going from $3 to $40 is not such a big deal. The cost of switches, encoders and faders plus case is much more. I may be better off starting with a prebuilt control surface and developing middleware for that. On the other hand, I might get used to mixing with rotary controls. I will try various knob sizes and feel. -- Len Ovens www.ovenwerks.net