Philip McKay via email
Many MIDI keyboard controllers feature a clutch of different velocity curves, such as these. From left to right, the linear setting is always a good starting point, but switching to the convex curve will give you greater control over louder notes, the saturated curve will deal with keyboards that won't otherwise generate maximum MIDI velocities, and the concave curve is the one to choose if the quiet end of the MIDI velocity range feels all 'bunched up' on your keyboard.
SOS contributor Martin Walker replies: Some keyboardists play harder than others, while keyboard controllers themselves can vary a great deal in their mechanical resistance, action and feel. If you come from a synth background, a weighted, hammer‑action keyboard may feel very heavy and ponderous to play while, conversely, if you're used to playing acoustic pianos, a lightweight, synth‑action keyboard may feel lifeless. However, the ultimate goal is always the same.
MIDI supports 128 different velocity values (from zero to 127) and, whichever velocity‑sensitive keyboard you choose, it should let each player generate this complete range of values smoothly as they dig into the keys, from soft to hard. This is the reason why most keyboards offer a selection of velocity curves.
Many modern sample libraries feature eight, 16 or even 32 velocity layers per note, and if your keyboard doesn't let you generate the full range of MIDI velocity values you may never hear some of these layers. This, in turn, means that your sounds may lack expression or sound dull or harsh, or it might mean that you never hear special effects programmed for high velocity values only, such as piano hammer noise, guitar harmonics or bass slaps.
It's generally best to start by trying the linear velocity curve that generates smoothly increasing velocity values as you play harder (see graph above). Some makes and models of controller keyboard do manage to do this over the full range but, in my experience, many don't generate any velocity over about 110, unless you hammer the keys really hard. The different curves stretch one or more velocity areas across the mechanical range. Don't get too hung up on the shapes themselves, it's more important to just play and see what velocity values you can generate.
You can choose the most expressive velocity curve by simply playing a favourite sampled instrument, such as a piano, but this can prove a tedious process. You may achieve the perfect response with 'loud' notes only to find that the soft notes now play too loud, or vice versa, or you may find that you only have the perfect response for that one instrument. It's better to be a little more systematic and monitor the MIDI velocity values themselves as you play, to check that you can move smoothly across the entire range. There are plenty of visual options for this purpose, including various sequencers that display incoming MIDI velocity as a level meter, or software utilities such as MIDIOX (see www.midiox.com for details).
Once you've chosen the most suitable preset curve for your playing style, a one‑off bit of final tweaking may make your keyboard playing even more expressive. For instance, my main controller keyboard smoothly generates MIDI velocities from 0 to 110, but struggles above this, so I just convert this input range to an output range of 0 to 127 using the MIDIOX Data Mapping function or a MIDI velocity-curve changer (see this one from www.trombettworks.com/velocity.php).
Most sequencers, and even some hardware/software synths, let you tweak incoming velocity values in this way, either using MIDI plug‑ins, such as VelocityCurveSM (www.platinumears.com/freeplugins.html for more information) or specialised built‑in functions, such as the Cubase MIDI Input Transformer. For a 'plug in and forget' hardware solution, you can buy a small box, such as MIDI Solutions' Velocity Converter (found at www.midisolutions.com/prodvel.htm), which is MIDI‑powered and offers 40 preset curves, plus a user‑defined one.
Some keyboards also include one or more 'fixed' velocity options that always generate the same MIDI velocity however soft or hard you play. These can be useful for playing sampled instruments with no velocity sensitivity, such as organs, and for step‑recording drum parts or simple synth tracks. A setting that always generates MIDI velocity 127 can also be invaluable for sound designers who need to ensure that their presets will never distort.
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