Synful Pitch Wheel
Portamento in Real String and Wind Playing
An important part of the expressive control exercised by a wind or string player involves controlling precisely how pitch changes from note to note and, in particular, how pitch changes during the transition from one note to the next. For example, when a violinist plays two notes of different pitches in succession she may choose to change the pitch in an abrupt manner or she may slide from the first pitch to the second by sliding her finger along the fingerboard in a continuous manner. This is called portamento. If the violinist slides from note to note on the same string without changing the bow then the portamento is very smooth with no discernable articulation of the second note. However, the violinist may also change bow direction at some point during the slide, the violinist may change the finger that depresses the string during the slide, or the violinist may change which string is bowed during the slide. In these later cases there can be an abrupt step in pitch and a pitch slide. There can also be an audible articulation with transient noise components marking the beginning of the second note.
For example, in a string portamento transition between two notes C and G, there may be an initial slide from say C to D, then a step from D to F#, and then a final slide from F# to G. This shape, consisting of slide-step-slide, is typical of many string portamenti. Controlling the rates and amounts of the slides, the size of the pitch step, and the character of the articulation when the pitch step occurs is central to expressive string playing. Wind instruments sometimes employ similar expressive control over portamento although not to the same extent as strings.
The Problem with MIDI Pitch-Wheel and MIDI Portamento
Standard MIDI synthesizers provide two controls that support pitch-slides: MIDI Pitch-Wheel and Midi Portamento Control. Suppose the performer wants to generate a slide-step-slide portamento transition as described above using the standard pitch-wheel. The performer can effectively perform the initial pitch-slide that occurs at the end of the first note. However, when the second note is struck the pitch jumps to the keyboard pitch plus the current value of the pitch wheel. If the performer quickly releases the pitch-wheel after striking the second note an undesirable quick slide back to the target pitch occurs. Alternatively, if the performer releases the pitch-wheel just prior to striking the second note there is an equally undesirable bend back to the first pitch before jumping abruptly to the second pitch. No matter how quickly and precisely the pitch-wheel is controlled the desired slide-step-slide curve is impossible to achieve.
The MIDI portamento control also does not support the generation of slide-step-slide pitch curves. The pitch shapes are deficient in two ways: first, the pitch slide does not begin until the second note is played on the keyboard; second, the pitch slides continuously from the first note pitch to the second note pitch – there is no step. Both MIDI portamento control and standard MIDI pitch-wheel curves are unacceptable.
The Synful Pitch Wheel Solution
Synful Orchestra introduces a special new Synful Pitch Wheel mode to solve the problems just described. The Synful Pitch Wheel mode can be turned on or off separately for each Program. Use the Synful Pitch Wheel switch found to the right of the Program Select box in the Synful Orchestra Control Panel. When the Synful pitch wheel switch is off (gray) the pitch wheel behaves like a standard MIDI pitch-wheel. When the Synful Pitch Wheel switch is on (red) Synful Pitch Wheel mode is entered for the program. The description of the special Synful Pitch Wheel mode sounds complex when described in words, but the actual behavior of the Synful pitch wheel is intuitive and natural. The user may choose to turn on Synful Pitch Wheel mode and start playing with it from a keyboard before reading the following description.
The special Synful Pitch Wheel mode is "context sensitive". When a first note is struck and then the pitch-wheel is displaced the pitch of the first note is “bent” in the standard manner corresponding to the position of the pitch-wheel. However, when a second note is struck, if there is little or no intervening time between the release of the first note and the strike of the second note then the response to the pitch-wheel during the second note is disabled. As a result, if the pitch-wheel is smoothly displaced in the direction of the pitch of the second note but prior to the strike of the second note, then the pitch slides in the direction of the second note. Then when the second note is struck the pitch steps in the direction of the second note.
If the pitch-wheel is released just prior to the strike of the second note then the pitch steps to exactly the pitch of the second note when the second note is struck. In this case a slide-step curve is generated. If the pitch-wheel is not released prior to the strike of the second note then the pitch steps part way to the pitch of the second note and then begins a slide up to the final second note pitch after the second note is struck. This is the slide-step-slide curve discussed above.
If the user bends the pitch-wheel while no keys are being held, and then plays a key, the note will be immediately bent as in standard pitch-wheel mode. The user can then gradually release the pitch wheel to create a normal attack with slide pitch bend effect.
Synful Pitch Wheel behaves naturally and intuitively whether playing single lines or chords and polyphony. However, there is one special case the user should be aware of when playing polyphony. If the user plays a chord and then bends the pitch all notes of the chord will be bent. Then if the user changes one note of the chord while not releasing the pitch-wheel, the other notes of the chord will be cut off. For this kind of polyphonic playing it may be better to turn Synful pitch wheel mode off.