Re: [LAD] [LAU] Ardour MIDI tracer

On Sun, 17 Aug 2014, Ralf Mardorf wrote: I don't know if it matters, but was that a linear fade or log? Right now with 1024 steps in the range around 0 where we would be doing most of our mixing (0 on the fader, about -4 signal?) it is 4 steps to go from -0.1 to -0.0, That is 0.025 of a db. Does that kind of fineness really need to be used for mixing? The problem is that the faders are linear, so with 127 levels, by the time you are down -20 you are 1 click per db instead .1db with 1024. So if you are mixing a hot level, for example, I often record my guitar raw and then add effects later which really adds to the level, so I may be mixing it in quite low, I have bigger steps in my control range. So Allen & Heath uses 127 levels on their top end digital control surfaces, How do they do it? Well they have two different scales: - fader: ((Gain+54)/64)*7f - also used for sends - Gain: ((Gain-10)/55)*7f - this is preamp gain I think in both cases only the 7f is hex (their chart is colour coded and hex numbers are blue, decimal are black). SO the fader has two clicks per db from -45 to +10 and the gain value seems to be 9 steps for 4 DB on the bottom (+10 to +22) and slowly increases towards +65 at the top where there are 12 steps for 5db. This means they are starting out with a linear value from the motorized fader (pot or encoder - if it was me it would be an encoder) and prescale it from a higher resolution, or they start with a log pot or encoder in the first place. The fact that they post the formula leads me to believe they do the former (though I think if it was me, I might have an encoder made with that built in). So the problem with 127 levels is not that it is too little so much as how those levels are applied. SO far as I know, all control surfaces on keyboards have linear CC values. The upside of using 127 levels is a lot less MIDI noise. Even though most interfaces not longer go at 30khz, most are 100meg or gig networks, bandwidth for a large number of channels still counts. (plus I think they run audio on there as well) It gets away from using pitchbend for faders with it's built in limit of 16. The upside of using 1024 (or more) levels: It is easy, no need to compute a level. Just like 192 samples/second, it makes for good advertizing. At some levels, it does give finer control... of course by the time you get to -40 or so, you have less resolution than scaled 127 level control. Pots vs. encoders: My preference for encoders is two fold. One, they have a very direct built in relationship between location and value. A pot will be different from one to the next and need to be callibrated once in a while (the Mackie controller has instructions for doing this). Two, there is no wear in the read area as a pot has with a wiper (assuming an optical encoder). They are expensive, but in a $25K control surface, I expect that kind of quality. A rotary encoder with 1024 pulses per rotation is about $50 in singles, One with 8 bits out and 256 states per rev is about $35. The ones used in most control surfaces with the push button are 24 clicks per rev and use mechanical contracts... but cost only $2.50 each, there are actually 96 clicks per rotation, but 4 clicks are required to sense direction (2 bit greycode) so it is possible to go for clicks for the first value and then assume the next click is the same direction from then on. The ones used in a mouse are even cheaper... -- Len Ovens www.ovenwerks.net