Thursday, December 23, 2021

TECHNIQUE: The Art of Sampling Part Four. Multi-Sampling. Velocity Mapping.


So we saw in Part Three how different samples need to be mapped across the keyboard to produce authentic, playable, and/or musical sampled instruments. That samples very often stop sounding like we want them to once we start moving away from the original sample's pitch. 

Well, we will very often need more samples, and employ another form of 'mapping' in order to arrange them. 

Velocity mapping allows us to sound different samples depending upon how fast a key or group of keys are struck. Whilst 'keyboard mapping' can be considered as the 'horizontal' mapping of a number of samples across a keyboard, 'velocity mapping' can be considered as the  'vertical' mapping of sounds/samples. 

We can take another look at our piano instrument from Bitwig's Sampler sample mapping editor:

You can see from this image that if you look at the sample zones above the keyboard there are three 'vertical' sample layers in addition to the 19 'horizontal' key mapping 'zones'. These are called 'velocity layers'. 

The reason we need velocity layers exists because of how musical instruments behave in the real world. Many instruments can be struck, plucked or hit either hard, soft, or any level in between. If we take a piano, as in the diagram above, for example, a note played 'hard' on a piano does not simply sound the same as the same note played softly. The 'timbre' of the sound changes. The same applies to many other instruments. Drums, acoustic guitar, electric pianos and all brass and wind instrument such as saxes, flutes, and trumpets. 

There are exceptions. Instruments such as organs and harpsichords can not actually be played at different velocities. Some modern organs may have velocity sensitive keyboards, but 'classic' organs such as a 'Hammond' or a Vox Continental could only be played at a single velocity. True, you could adjust the swell pedal for more or less volume, but the timbre always remained the same. Harpsichords are also only 'plucked' at a single velocity, so a single velocity layer can (and should) be employed for recreations of these instruments. 

So you can see for our piano sound above, three velocity layers are employed. A 'soft' layer (p/mp, pianissimo/mezzo-pianissimo), a medium layer (mf, mezzo-forte) and a 'hard' layer (f, forte). This will give us good degree of realism although more layers can be employed for greater detail and realism.

Keyboard velocity is usually measured from 0-127, so a typical arrangement for a piano instrument might be 0-64 (soft, p, mp), 65-110 (medium, mf), and 111 - 127 (hard, f). 

At this point we are only 'switching' between the layers depending upon how hard a key is struck, however, many sample players/editors allow us to 'crossfade' between velocity layers. Rather like 'crossfading' between key zones, velocity layer scan often employ crossfading so the different layers 'merge' softly.    

Of course, velocity layers don't have to be used just for realism. With synthesizer type sounds, for example, different elements can be added depending upon how hard (or more accurately, how fast) a key is struck. Timpani could be added to a string ensemble type sound at higher velocity levels. The possibilities are endless!

Thank you for checking out this post in the series, I hope you found it useful. 

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