Programming Manual: Programming
- Process of Programming
- Parameter Value Ranges
- Copy Modes
- "Scratch" Patch
- Control Signal Scaling
The Chroma's memory contains fifty stored programs (and one current program), each of which is a complete description of a sound. Each program is made up of a set of parameters, each of which controls one aspect of the sound, just like a slider, knob or switch on an ordinary synthesizer. In the Chroma, every parameter has both a name and a number. The name describe the parameter for the user, and the number identifies it for the Chroma's computer. Each parameter also has another number associated with it: its value. This is like the setting of a switch or position of a slider. Different parameters have different numbers of possible settings, depending upon what they do. Parameters have as few as two settings, such as the low-pass/high-pass selection on the filter, while others have as many as 128 settings for accurate resolution of critical adjustments of the sound. Each program contains 101 separate parameters, which are divided into four groups, called panel, control, A and B.
- Panel Parameters do not directly participate in the description of a sound. Rather, the panel parameters reflect the settings of certain modes on the control panel. These parameters are included in each program so that the settings will be automatically initialized each time a program is selected.
- Control Parameters are part of the description of a sound. They include those parameters that pertain to the entire sound, not just one of a pair of channels.
- "A" Parameters describe the sound produced by a single channel. If the program utilizes one channel per note, the control parameters and A parameters will completely describe the sound. If the program utilizes the channels in pairs, the control parameters affect both channels and the A parameters affect only the A channels.
- "B" Parameters are used only when the program utilizes channels in pairs. The set of B parameters is identical to the set of A parameters, and controls the B channel in each pair.
Whether the program uses single channels or paired channels is determined by one of the control parameters, called PATCH . If the program is set up to use individual channels, the B parameters still exist in the program, but they have no effect on the sound generation.
The Chroma control panel has all the capability needed to recall, view, modify and save all 101 of the parameters in all 51 programs.
The left panel parameters are accessed using their own dedicated controls. In a sense, they are all performance controls, as their easy accessibility promotes their use during performance.
The control, A and B parameters are all accessed by one uniform method, involving the parameter control slider, the 8-digit display, the EDIT A and EDIT B switches. The 50 numbered switches on the right panel are also used, under the three aforementioned panel modes, PARAMETER SELECT, COPY FROM A and COPY FROM B.
The 50 numbered switches on the right panel that are used for selecting programs are also used for selecting parameters to be modified. Each switch, in addition to having a number imprinted on it, has the name of a parameter on it. The switches numbered 1 through 5 are associated with the five control parameters in the program. The remaining 45 switches identify A and B parameters. Rather than include a separate set of 45 switches for the B parameters, the A and B are accessed using the same set of switches along with the EDIT A and EDIT B switches.
The parameter control slider is always "connected to" one of the parameters in the program (or to a pair of A and B parameters). The number of the switch that corresponds to that parameter will appear in the left half of the 8-digit display, and the current value or setting will appear in the right half of the display. Moving the slider will cause the setting to change.
Changing the value of the selected parameter (the one that appears in the display) can be done at any time by moving the parameter control slider. Selecting a different parameter number can only be done by first entering PARAMETER SELECT mode. In this mode, the 50 numbered switches no longer cause a program to be selected, but cause a parameter to be selected instead. This is the mode used most often in programming.
Different parameters have different ranges of control. Some parameters represent selector functions, where each setting selects something unrelated to the other settings. The simplest form of this is the two-position switch. The GLIDE SHAPE  parameter is an example of this. This parameter has two settings, 0 and 1. Moving the slider through its center position causes the value to change, and causes the panel tapper to be triggered, giving a little tactile feedback. Some selector parameters have as many as 16 settings. Moving the slider will take the parameter through all its settings, triggering the tapper at every change, as if it were a 16-position slide switch with detents. Many parameters, however, are variable parameters which describe something that has a variable quantity, such as a modulation or tuning. The tapper does not get triggered when the slider is used to change a variable parameter. Some variable parameters are unipolar, such as the oscillator TUNE  parameter which has a range from 0 to 63. Most of the modulation depth parameters, on the other hand, are bipolar, with a range from -64 to 63, with 0 in the middle.
If one of the five control parameters is selected, the EDIT A and EDIT B switches have no effect on what the parameter slider is connected to, as there is only one set of control parameters. If one of the remaining 45 parameters is selected, the EDIT A and EDIT B switches are used to select whether the A or B parameter is connected to the slider. When a parameter is first selected (see below), its setting has nothing to do with the slider position. As soon as the slider is moved, the parameter jumps to the value represented by the position of the slider. A special mode called EDIT A & B mode can be selected by pressing the EDIT A and EDIT B switches concurrently. In this mode, the initial display shows the setting of the A parameter, but moving the slider causes both the A and B parameters to jump to the same value and follow the slider.
The COPY FROM A and COPY FROM B modes are used to copy parameters from one program to another. These two switches are identical in function except that one mode causes parameters  through  to be copied from the A group of parameters in the source program while the other mode causes parameters  through  to be copied from the B group of parameters. Thus it is possible to copy an A parameter in one program into the corresponding B parameter in the current program. Pressing one of the copy switches causes its LED to flash, meaning that the Chroma is waiting to be told what program to copy from. The next numbered switch pressed causes the corresponding program to be selected as the source for parameter copying, and causes the copy mode to be entered. Subsequently, pressing a numbered switch causes the corresponding parameter to be selected and initialized by copying its setting from the stored program. A special facility is provided for copying from the current program. Pressing COPY FROM A twice sets the COPY FROM A mode, using the current program as the source. If EDIT B is active, each parameter selected will be copied from the A group into the B group in the current program. Likewise, pressing COPY FROM B twice with EDIT A active allows copying parameters from the B group into the A group in the current program.
Copy from A or B Sequence
- Press [COPY FROM A] (or B) (Light Flashes)
- Press any program number you wish to use as a program source.
- Press the parameter number you wish to copy data from (data is automatically copied).
- Press [PROGRAM SELECT] or [PARAMETER SELECT] to get out of copy mode.
There is a parameter called OUTPUT SELECT , which routes the channel output (both channels if paired) to one of the four outputs labelled 0-3. If the channels are paired, the B oscillator can be tuned up to 31/32 semitone, in 1/32 increments (which is useful for bringing odd ring-mod intervals in tune). The FSW MODE  parameter allows selective disabling of either footswitch, and allows the left footswitch to be used to enable or disable the playing of notes (useful when linking). And the KYBD ALG  parameter selects one of 16 possible channel assignment algorithms, five of which are polyphonic, and eleven of which are monophonic. See the Table of Parameters for greater detail.
Another useful feature provided is the parameter clearing feature. Holding one's finger on the PARAMETER SELECT switch while selecting a parameter causes the parameter to be initialized to 0. There are a few exceptions to this: the pitch TUNE parameter is initialized to 12, which is concert pitch, and the cutoff TUNE, envelope 1 and 2 DECAY and volume MOD 1 DEPTH are set to their full settings. Therefore, if all parameters are cleared, there will be some sound (a raw sawtooth, a good enough place to start). In this mode, or in either copy mode, a whole group of parameters can be quickly initialized by running a finger across a row of numbered switches.
The whole business of the actual quantities involved in control signal generation and use is pretty simple. The old modular synthesizers used one volt per octave as the standard relationship between control signal level and frequency. Also, they used ten volts as the standard size of any control signal. The principle is the same in the Chroma, although the numbers have been changed. The user doesn't need to be concerned with "volts" in the Chroma. Instead, everything is measured against an arbitrary "unit." The rules are as follows:
One unit can be thought of as equalling 32 semitones of pitch. This is because the glide output is scaled this way. The glide output has a range from -1 unit too almost +1 unit, with 0 at middle C. The range is extended 12 semitones (3/8 unit) each way with the transpose switches.
The levers also have a range of -1 to +1 units, where positive numbers are in the "push" direction.
The bipolar sweep waveshapes (sine, triangle, saw, etc.) have a smaller range, from -½ to +½ unit.
The envelopes are 1 unit in amplitude without touch sensitivity, but vary from 0 to 2 units in amplitude with touch sensitivity.
The pedals, velocity, and pressure all go from 0 to 1 unit.
When control signal parameters are themselves modulated by other control signals (such as using a pedal to control decay time), the programmer has no choice as to the depth. It is fixed, hopefully at a useful level.
The filter modulation depths represent the number of semitones tuning change for each unit of modulation. Obviously, a setting of 32 represents unity gain if the glide source is used. The ability to set the depth from --64 to +63 yields a gain range from -2 to almost +2.
The pitch modulation 3 depth is scaled like the filter. MOD  has 1/4 the gain, the MOD  has 1/16 the gain. If MOD  is used for pitch bend, the depth parameter will be the number of semitones in each direction that the lever will bend the pitch.
Certain "standards" of usage seem to be appropriate for an instrument that can be patched so many ways:
- Lever 2 will most commonly be used for pitch bending. Lever 1 will be used first for other effects, such as vibrato depth (sweep amplitude modulation). The pitch bend range and polarity should be consistent. A whole tone in each direction, with the pitch increase in the "pull" direction is a useful setting.
- Pedal 1 will most commonly be used for volume control. Pedal 2 will be used first for other effect, such as filter tuning.
- The modulation inputs to the oscillator are each scaled differently. Vibrato will usually go to input 1, while large envelopes will usually go to input 3.
- The filter modulation inputs are all scaled the same, yet pitch tracking (glide modulation) will usually go in on input 1 while sweep modulation will usually be assigned to input 3.
- All parameters that don't have any effect will be in their clear state.
- All panel parameters should be set to something appropriate when a program is stored. Most importantly, the parameter control slider (and edit mode switches) should be left connected to something useful. All the link settings should be consciously set, even if they are not being used. In particular, the keyboard split should be set to some standard (such as -5), and the program should be linked to itself and then unlinked, leaving the link program number reset. The link balance should be set to zero.
- The annual Chroma convention will be held in Lubbock Texas on September 31, 1982. Ballots must be submitted for the High Parameter, and the Big "C" by August first. Apple IIs should be worn. Contact the Program Wizard for details.
Certain commonly useful programming structures are:
- Using two low-pass filters in series for a four-pole low-pass response (good for brass).
- Using two low-pass filters in parallel, tuned several octaves apart (for rather vocal effects).
- Using a low-pass and a high-pass in series for a band-pass sound, possibly with two separate resonant peaks (great for clav sounds).
- Using a low-pass and a high-pass in parallel for a notch sound possibly modulating them with a slow sweep (also great for clav or harpsi sounds).
- Using glide to modulate the pitch. The glide always feeds the oscillator pitch input, so adding glide modulation can expand or compress the scale. This is especially useful on oscillator B when it's synced to oscillator A.
- Making the sweep rate (and perhaps amplitude) track the keyboard, and then using the sweep sine wave to modulate the waveshape. This can create a chorus effect that sounds right across the whole keyboard.
- Using a pedal for pitch bend, and either the other pedal or the pressure for vibrato depth.
- Using the velocity to directly modulate the filter tuning, instead of controlling the amplitude of an envelope.
- Using the normal and inverted pedal modulation selections on the amplifiers, to pan between the A and B channel.
- Using the delayed envelopes 2A and 2B to generate two echoes after the initial attack. The three attacks that result can all differ.
- Using polyphonic filtering of noise for spectacular wind effects.
- Simulating a phase shifter with a sweeping notch.
- Creating string section sounds that grow and fade according to the key velocity.