17. Csound on BP2 -- a primer
17.1 What is Csound, how does it relate to BP2?
Unlike hardware sound processors, Csound
puts no limitation to the number of instruments and the complexity of their
processes. Indeed, a sophisticated orchestra file would request a great deal of
computation time, but it remains workable on small computers whenever speed is
not critical.
With recent hardware enhancements
(multiprocessing, RISC...) Csound has become fast enough for real-time
synthesis, making it possible to adjust various sound parameters interactively.
In other words, musicians can explore sound spaces rather than rely on
speculations as to what a certain formula would yield. This shift from theory to
practice is giving Csound a second life at a time computer users feel allergic
to batch-processing techniques and dream of immediate feed-back and interactive
systems.
Csound works with two input files, the "orchestra
file" and the "score" file, both in comprehensive text format.
This makes it easy to musicians to share a broad library of sound design "recipes",
a sample of which is supplied with the software itself.
BP2 may create a piece of music in the
real-time MIDI environment and then enhances it with Csound. Csound and BP2 are
similar and complementary in their text-oriented, programming approach, with
respective emphasis on sound and musical structures. None of these programs
make assumptions on the musical system even though they optionally accept
practical conventions such as "octave point pitch-class"
representation in Csound, or "simple notes" in BP2.
A Csound instrument is the procedural
representation of computational processes at the lowest level; conversely, a BP2
sound-object is a declarative representation of elementary events and properties
at a more abstract level.
While Csound is quite user-friendly for
the description of instruments (the "orchestra file"), it does not
offer any in-built facility for the design of event lists (the "score"
file). Score files are usually typed or produced with higher-level algorithms
such as the ones programmed with Cscore, a utility
supplied on the same site. But not every musician is a C programmer... A
convenient way of generating Csound scores is to convert them from MIDI files,
but this limitates Csound parameters to the very few ones implemented in MIDI.
BP2 handles any number of parameters (with arbitrary names) that may be assigned
any position among Csound instrument arguments.
(Subject to confirmation by Csound
folks
) BP2 is to-date the most advanced program for the creation of Csound score
files. BP2's input may be comprehensive text scores (with an alphabet of simple
notes and sound-objects) or music production processes such as grammars or
scripts. BP2 attempts to take full advantage of the versatility of Csound,
by-passing the limitations of MIDI.
In the following examples (except §17.5)
we are using imaginary orchestra files and proposing a visual, rather than
sonic, verification. The reason is that we intend to demonstrate a great
variety of parameter formats.
17.2 Producing Csound scores with BP2
First select the "Csound" option in the "Output" menu. This option
is saved with the settings of the current project or data. If the "MIDI"
option is still active, musical items will be played on MIDI and then the user
will be prompted to go for a Csound score. If "MIDI" is inactive
Csound scores are immediately saved to a file. (See more options Fig.33.)
If Csound is running on a Unix or
Windows machine it is a good idea to change the file format to "DOS"
or "Unix". The dialog for MIDI and Csound file saving options is
visible after typing cmd-option space ("Settings" in the "Windows"
menu).
On the top "Settings" dialog,
checking "Trace Csound" requests BP2 to
display a copy of the score in the "Trace" window. A good idea for a
first check-up.
BP2 creates a Csound score of musical
items selected in a text window (a "BP2 score")
or produced by a grammar. The components of these musical items are
sound-objects and/or simple notes. A sound-object contains a sequence of
elementary events that may be described as a MIDI stream, a Csound score, or
both.
In the latter case, BP2 checks that the
durations of the MIDI and Csound sequences are identical. It makes sense to
have both descriptions generate similar sounds on MIDI and Csound, so that MIDI
is used for an immediate check and Csound for the final material.
- When sound-objects contain Csound scores,
their MIDI streams are ignored and the final score
is a rearrangement of these score lines with appropriate changes in the timings
of events and the values of their parameters. (See §17.8)
- When a MIDI stream is used as the input (which is
always the case with simple notes), BP2 does its best to convert MIDI messages
to Csound score lines. (See §17.3)
In both cases BP2 needs information
about the parameter locations and ranges for each instrument of the Csound
orchestra file. Unfortunately, reading the orchestra file would not yield the
required information unless it is prepared in a comprehensive way. (Csound
designers might think of new instructions in Csound orchestra files that would
make this information directly accessible :-) This partial description of Csound
instruments is entered in the "Csound instruments" dialog and saved to
a "-cs.<name>" file.
Version 2.9.3 of BP2 inserts function
tables into the score when necessary, thus enabling arbitrary variations of
continuous parameters within a single Csound event (a score line).
17.3 Try Csound with simple notes
Select the "Data" window and
type cmd-o to load "-da.tryCsound" in the examples folder. On top of
the "Data window" the instruction
-cs.tryCsound
tells BP2 to immediately load the "-cs.tryCsound" file describing the orchestra. Since no "-mi.<name>" is attached, musical items will contain only simple
notes, and Csound scores will be based on the conversion of MIDI messages.
Select for instance the sequence of
simple notes
A4 G4 C5 A4
and type cmd-p ("Play selection"). This item is played on MIDI and immediately saved
to a Csound score file containing:
t 0.000 60.000
i2 0.000 1.000 440.00 90.000
0.000 0.000 0.000 ; A4
i2 1.000 1.000 392.00 90.000
0.000 0.000 0.000 ; G4
i2 2.000 1.000 523.25 90.000
0.000 0.000 0.000 ; C5
i2 3.000 1.000 440.00 90.000
0.000 0.000 0.000 ; A4
s
Each line starts with "i2"
meaning that instrument 2 is used. BP2 found this value in the settings of
instrument 2:
Assign as default to channel 1
and MIDI channel 1 is the one used by
default.
On each score line, the "2" of
"i2" is the value of argument 1, the leftmost one. The next two
arguments are always assigned to the on-setting date and duration of the event,
measured in beats. Then comes argument 4, which in this example is assigned to
pitch, here in cycles per second. Argument 5 is the volume (range 0..127) set
to 90 by default. Arguments 6, 7 and 8 are used for another parameter not
demonstrated here.
Instrument 2 does not accept any other
parameter. Therefore, velocity, pressure, modulation, etc., assignments are
ignored.
17.4 Describing a Csound instrument
Look at the "Csound instruments"
dialog accessible from the "Output" menu. Instrument 3, which (for fun) we named a "Harpsichord",
is shown Fig.34.
Fig.34 Describing a Csound instrument in the BP2
environment
This instrument assigns pitch to
argument 4 but it uses the "cps (Hz)" frequency representation.
Further, it assigns pitchbend to arguments 5 and 6. Why two arguments? Since
pitchbend may vary continuously, it is smart to supply the values at the
on-setting and off-setting dates so that Csound may do something with it. There
is an empty square to the right of these arguments, just after the question
mark. It may contain another argument index for passing on tabulated functions
to Csound when movements become more complex. (Since BP2 does it automatically,
you don't have to bother about understanding Csound function tables.)
In MIDI a NoteOn starts a process, a
NoteOff terminates it, and between the two the sound generation may be modified
in real time by control messages. But in a Csound event all arguments are
supplied in advance. Therefore, it is the task of the instrument procedure to
modify its own parameters. If only start and end values of the control
parameter are supplied, Csound has no other option than perform a simple
interpolation. However, with sound-objects additional information may be passed
on to Csound (see §17.11).
Arguments 7 and 8 of this bizarre
harpsichord are used similarly for continuous volume control. In addition, MIDI
values in range 0..127 are mapped to the range -24..24, which is declared a "logarithmic"
scale. Here we assumed that "Harpsichord" would takes decibels as a
volume input value. Since performance control _volume(x) uses the MIDI range
0..127, a remapping is automatically done by BP2 on the basis of three supplied
pairs of values.
A similar mapping is applied to
modulation (arguments 11 and 12) and panoramic (argument 13) parameters. Since
the latter has only one argument it cannot be used in continuous variation with
this instrument.
Csound argument mapping is explained in
BP2 reference manual (§9.1). All you need to know is that the first line
contains three input values and the second one the three corresponding output
values. BP2 manages to find a proper quadratic and/or linear interpolation
matching these points. Error messages are displayed in rare cases when the
mapping is impossible.
The input, output, or both input and
output scales of the mapping may be declared as "logarithmic" for a
more meaningful conversion.
Let us for instance produce a Csound
score for the musical item:
_ins(Harpsichord) _volumecont
_volume(127) A4 G4 C5 A5 A4 G4 C5 A5 _volume(0)
which specifically invokes instrument 3,
using its name, and allows the volume to vary continuously from 127 to 0. The
Csound score is:
t 0.000 60.000
i3 0.000 1.000 440.00 8191.500
8191.500 24.000 21.688 0.000 0.000 0.000 0.000 0.000 ; A4
i3 1.000 1.000 392.00 8191.500
8191.500 21.688 18.431 0.000 0.000 0.000 0.000 0.000 ; G4
i3 2.000 1.000 523.25 8191.500
8191.500 18.431 12.899 0.000 0.000 0.000 0.000 0.000 ; C5
i3 3.000 1.000 880.00 8191.500
8191.500 12.899 -0.031 0.000 0.000 0.000 0.000 0.000 ; A5
i3 4.000 1.000 440.00 8191.500
8191.500 -0.031 -1.179 0.000 0.000 0.000 0.000 0.000 ; A4
i3 5.000 1.000 392.00 8191.500
8191.500 -1.179 -2.794 0.000 0.000 0.000 0.000 0.000 ; G4
i3 6.000 1.000 523.25 8191.500
8191.500 -2.794 -5.547 0.000 0.000 0.000 0.000 0.000 ; C5
i3 7.000 1.000 880.00 8191.500
8191.500 -5.547 -24.000 0.000 0.000 0.000 0.000 0.000 ; A5
s
The column of argument 4 (pitch) is
self-explanatory. Arguments 5 and 6 contain the constant default value of
pitchbend (8191.5). Arguments 7 and 8 are the ones showing the volume
decreasing from +24 to -24. Arguments 11, 12 and 13 keep their default values.
Arguments 9 and 10 are used by another parameter (see 'blurb' infra) here set to
0.
Important
If you use the "cps (Hz)"
frequency representation, do not forget to "tune" BP2 in case the
diapason frequency is not 440Hz. (See §4.8.)
So far we demonstrated that parameters
mapped to MIDI controls, i.e. pitchbend, modulation, volume, panoramic and
pressure, can be controlled continuously and mapped to Csound parameters. More
parameters, specific to Csound, may be defined in the dialog accessed clicking
the "MORE..." button (see Fig.34). There is room for six additional
parameters in each Csound instrument, a total 250 in the entire orchestra.
Fig.35 Description of additional Csound instrument
parametersEach additional parameter has a default
value which is not necessarily zero. Values found on Csound scores may be
combined additively (ADDval) or multiplicatively
(MULTval). Tables describing fine variations of the
parameter may use arbitrary Csound generators. GEN07
(linear interpolation) is assigned by default, but GEN08
(cubic spline) may be prefered in some cases.
Additional parameters are given
arbitrary names. They are controlled by instructions "_value(param,x)", "_step(param)",
"_cont(param)" and "_fixed(param)". An example in "-da.tryCsound" demonstrates the control of an arbitrary parameter
labelled 'blurb' which is recognized by both instruments "Harpsichord"
(3) and "Flute" (2).
_ins(Harpsichord) _cont(blurb)
_value(blurb,123.42) C4 D4 _ins(Flute) E4 F4 _value(blurb,-211) _step(blurb) G4
A4 _value(blurb,-34) _fixed(blurb) B4 C5
i3 0.000 1.000 261.63 8191.500
8191.500 16.981 16.981 123.420 39.815 0.000 0.000 0.000 ; C4
i3 1.000 1.000 293.66 8191.500
8191.500 16.981 16.981 39.815 -43.790 0.000 0.000 0.000 ; D4
i2 2.000 1.000 329.63 90.000
-43.790 -127.395 0.000 ; E4
i2 3.000 1.000 349.23 90.000
-127.395 -211.000 0.000 ; F4
i2 4.000 1.000 392.00 90.000
-211.000 -211.000 0.000 ; G4
i2 5.000 1.000 440.00 90.000
-122.500 -122.500 0.000 ; A4
i2 6.000 1.000 493.88 90.000
-34.000 -34.000 0.000 ; B4
i2 7.000 1.000 523.25 90.000
-34.000 -34.000 0.000 ; C5
Additional parameters take any values in
floating-point format, but they cannot be remapped before being sent to Csound
instruments (see reference manual §9.1 regarding remapping). The use of
control parameters K1, K2... is not licit in the
current version of BP2.
17.5 Checking the Csound output
A Csound orchestra file named "BP2test.orc" is supplied. It works with any Csound score
produced by BP2 in the absence of a Csound instrument description file (-cs.<name> file).
Below is the listing of the
default orchestra file.
; This is a simple orchestra
file for BP2's default Csound score output
; It follows the new
specfications handled by BP2 version 2.7.2 and above.
; (See "Csound tables")
; It contains one single
instrument: an oscillator using wave-table 1
; Argument p2 is the start date,
p3 the duration (as per the standard)
; Argument p4 is the pitch in
octave point pitch-class format
; Volume (range 0..127) is
supplied by performance control _volume()
; to arguments p5 (beginning
value) and p6 (end value), or via the table
; whose index is supplied by p7.
; Pitchbend is supplied in cents
to arguments p8 (beginning value)
; and p9 (end value), or via the
table whose index is supplied by p10.
sr = 22050
kr = 2205
ksmps = 10
nchnls = 1
instr 1
ik1 = 32767. / 127.
ik2 = log(2.) / 1200.
ifvol = p7
ifcents = p10
kvol line p5, p3, p6
if (ifvol <= 0) goto
volumelin
ilenvol = ftlen(ifvol)
kndxvol line 0, p3, ilenvol
kvol tablei kndxvol, ifvol
volumelin: kcents line p8, p3,
p9
if (ifcents <= 0) goto
pitchbendlin
ilencents = ftlen(ifcents)
kndxcents line 0, p3, ilencents
kcents tablei kndxcents, ifcents
pitchbendlin: kpitch =
cpspch(p4) * exp(kcents * ik2)
kamp = kvol * ik1
a1 oscil kamp, kpitch, 1
out a1
endin
This code should not look esoteric to
Csound users. The unique instrument in this orchestra is an oscillator
controlled in volume by arguments 5 and 6 (start and end respectively) and in
pitch by argument p4 (octave point pitch-class format). Pitchbend corrections
are given in cents by arguments 8 and 9 (start and end respectively). In
addition, arguments 7 and 10 may contain the references of function tables when
complicated variations are described.
We are confident that Csound users will
pick up the idea and develop their own instruments taking advantage of BP2
features such as panoramic control, and any additional control they think
useful. We hope that convincing examples will be shared between users.
Type cmd-n ("New Project") to
flush the current Csound orchestra description and use the default instrument
exclusively. Then load "-da.Csoundtest" in
the "Data" window.
_volumecont _pitchcont
_pitchrange(200) _volume(30) C5 _volume(127) D5 _pitchbend(100) E5 F5
_pitchbend(0)
Select this item and type cmd-p ("Play
selection"). Save the resulting score as "BP2test.sco":
; Csound score
f1 0 256 10 1 ; This table may
be changed
t 0.000 60.000
i1 0.000 1.000 9.00 30.000
127.000 0.000 0.000 0.000 0.000 ; C5
i1 1.000 1.000 9.02 127.000
127.000 0.000 0.000 0.000 0.000 ; D5
i1 2.000 1.000 9.04 127.000
127.000 0.000 100.000 50.000 0.000 ; E5
i1 3.000 1.000 9.05 127.000
127.000 0.000 50.000 0.000 0.000 ; F5
s
e
; this score was created by Bol
Processor BP2 (version BP2.7.2)
To close the score file, type cmd-option
space (window "Settings") and uncheck "Write csound scores". Now you may open the score with Csound. (If the
computer does not have enough memory, first quit BP2.)
Tell Csound to create a sound file using
"BP2test.orc" and "BP2test.sco". Listen to the result. (Nothing great. It just
works.)
If you are not happy with the buzz you
may try to change the waveform in table 1, as explained in §17.6. Apart
from being extremely dull, a sine-wave oscillator may yield weird results when
several notes are superimposed. Since BP2 provides Csound with events timed
within 1ms accuracy, phasing effects modify considerably the perceived balance
of mixed sounds.
Beware of computation overflows occuring
at the time Csound processes the score file. These are displayed at computation
time. It is wise to use _volume(x) with a proper value of 'x' in range 0..127
so that saturation is avoided. A simple method consists in dividing the
maximum volume (127) by the estimated number of simultaneous voices, and use the
result as a maximum volume for each voice. Use
control parameters _volume(K1), _volume(K2)...
to avoid repeating numeric data (see §1.9).
17.6 Csound function tables describing waveforms
Most Csound instruments need tables to
produce wave-forms, ramps, etc. These tables are stored by BP2 along with the
-cs.<name> file and may be accessed clicking the top left button "Tables..."
on the Csound instrument dialog (see Fig.34). Default table "f1" is
written following the syntax of Csound:
f1 0 256 10 1
It contains 256 points and uses GEN10
(the harmonic oscillator) with only the first partial, yielding a sine-wave.
This is the default table used by BP2.
Csound waveform descriptions are automatically inserted in the beginning of Csound
score files. They are not displayed in the "Trace" window even when "Trace
Csound" is active. Do not use indexes beyond 100
as these are reserved to function tables automatically produced by BP2 (see §17.12
infra).
17.7 Sound-objects containing Csound scores
Sound-objects contain sequences of
elementary events which may be described as a MIDI stream, a Csound score or
both.
When BP2 is instructed to produce MIDI
real-time or a MIDI file, it uses the MIDI stream of sound-objects and ignores
their Csound definitions. Conversely, when asked to write the performance as a
Csound score, it uses the Csound score of each sound-object. If the
sound-object has no score, BP2 converts its MIDI stream to a Csound score, using
the current or default Csound instrument description, as shown in the preceding
section.
To produce Csound scores it is wiser to
design Csound scores in sound-object prototypes rather
than rely on a conversion from MIDI which may leave out relevant parameters.
A demo of the use of sound-objects
containing Csound scores is given in "-da.tryCsoundObjects". Type cmd-e ("Edit prototypes") to load
the attached "-mi.tryCsoundObjects"
sound-object prototype file. Then click button "Csound" to display
the Csound score of prototype 'a' (see Fig.36).
Fig.36
The Csound score of a sound-object prototype
The score contains four events invoking
instruments 1, 2 and 3. Note that this score is incomplete because it contains
only the compulsory arguments for setting time, duration and pitch. BP2 will
complete missing arguments with their default values.
To compile this score, BP2 requires the
description of instruments supplied by the "-cs.tryCsoundObjects" Csound instrument file. This file has been loaded
automatically for two reasons:
- Its name appears on top of the "-da.tryCsoundObjects" file
- Its name has been found in the "-mi.tryCsoundObjects" file (on the left top of the window, see Fig.36).
It can be changed by clicking the "Change instrument file"
button.
To avoid inconsistencies it is
sufficient to state the name only once, preferably in the sound-object prototype
file.
On the graphics Csound events are marked
with red lines whereas MIDI events show as black lines. Objects 'a', 'b' and
'c' in this file contain only Csound scores (as told by radio buttons on
Fig.36), whereas the sound-object prototype 'midiobject' also contains a MIDI
stream. The MIDI stream and the Csound score of an object may contain similar
events as to pitch and timing, but each of them may also contain additional
information that is specific to the representation: Csound score lines contain
parameters that have no equivalent in the MIDI stream, and conversely a few MIDI
messages may not be reflected in a Csound score.
BP2 checks that the Csound score and the
MIDI stream, if not empty, represent sequences of events with identical
durations. If this is not the case a message is displayed although the user is
not forced to correct the mismatch. In this case, the longest duration is taken
as the nominal duration of the sound-object prototype.
17.8 Creating a Csound score in a sound-object prototype
There are three ways of creating a
Csound score describing the sequence of events in a sound-object prototype.
- Type the score in the window displayed Fig.36;
- Import the score from a text file (which could as
well be a score produced by BP2);
- Create the score by converting the MIDI stream to
Csound.
The third method is a practical way of
converting BP2 projects from MIDI to Csound. First of all, a Csound instrument
file such as "-cs.tryCsoundObjects" must be
loaded so that the conversion makes use of the proper instruments. Then, for
each sound-object prototype, click the button "Convert to Csound". If necessary, the MIDI stream may be deleted
afterwards: click "Edit/record MIDI stream"
and "CLEAR".
Needless to say, sound-objects
containing a Csound score may be granted the same properties: pivot, continuity,
periodicity (§2.5) etc., as the ones containing a MIDI stream. Thus,
Csound users can benefit of advanced features of BP2 as to timing, constraint
satisfaction, etc.
17.9 Performing musical items in the Csound environment
For instance we request BP2 to perform
{a,b} c
with sound-object prototypes a, b, c
containing the following Csound scores:
Score for a
t 0 120
i1 0 0.5 4.05 ; F0
i1 0 0.5 4.05 ; F0
i2 1.5 0.5 5.05 ; G5
i3 1.5 0.2 643.5 1 ; D#5
e
Score for b
t 0 60
i3 0 0.8 461.34 1; A4
i4 0.1 0.2 6.03 1.05 ; C2
e
Score for c
t 0 120
i2 0 0.2500 9.00 0 0 90 90 ; C5
i2 0.2500 0.2500 9.02 0 0 62 62
; D5
i2 0.500 0.2500 9.04 0 0 90 90 ;
E5
i2 0.7500 0.2500 9.05 0 0 90 90;
F5
e
Properties of these sound-objects are
the default ones except for 'b' which has its pivot delayed 20% of its duration
The final score (see below) is a
combination of the prototype scores shown above. It reads:
t 0.000 60.000
i3 0.000 0.800 461.34 1.000 ; A5
i4 0.100 0.200 6.03 1.050 ; C2
i1 0.160 0.250 4.05 90.000
90.000 0.000 0.000 0.000 0.000 ; F0
i1 0.160 0.250 4.05 90.000
90.000 0.000 0.000 0.000 0.000 ; F0
i2 0.910 0.250 5.05 0.000 0.000
90.000 90.000 0.000 0.000 0.000 ; F1
i3 0.910 0.100 643.50 1.000 ;
D#6
i2 1.160 0.125 9.00 0.000 0.000
90.000 90.000 0.000 0.000 0.000 ; C5
i2 1.285 0.125 9.02 0.000 0.000
62.000 62.000 0.000 0.000 0.000 ; D5
i2 1.410 0.125 9.04 0.000 0.000
90.000 90.000 0.000 0.000 0.000 ; E5
i2 1.535 0.125 9.05 0.000 0.000
90.000 90.000 0.000 0.000 0.000 ; F5
s
BP2 appends note names as remarks to
events that invoke a pitch-sensitive instrument: 'A5', 'C2'...
Note the changes on timings in the score
lines borrowed from sound-object prototypes 'a' and 'c'. These objects have
been performed at tempo mm = 60 while their own reference tempo was mm = 120.
Since Csound represents time in numbers of beats, their relative durations have
been divided by 2.
It may look abnormal that all on-setting
dates (except for the first two events) have been delayed by 0.160 beat. The
explanation lies in the time setting of the musical item recalling the
particular pivot location of sound-object 'b' (see Fig.37).
Fig.37
The time setting of "{a,b} c"
17.10 Performance controls and Csound scores
Other examples in "-da.tryCsoundObjects" demonstrate modifications of Csound argument values
caused by performance controls. Try for instance:
_pitchrange(200) _pitchcont
_volumecont _volume(30) _pitchbend(0) a C4 D4 b c _pitchbend(100) _volume(127)
containing sound-objects 'a', 'b', 'c'
and simple notes 'C4' and 'D4'. Simple notes are set on the default MIDI
channel 1 which is also assigned instrument 1 as shown in "-cs.tryCsoundObjects".
The graphic score is shown Fig.38.
Fig.38
The time setting of "a C4 D4 b c"
The different instruments called to
perform the resulting sequence of events have various ways of dealing with
pitchbend and volume controls. For instance, instruments 3 and 4 do not control
pitchbend continuously but they take the current value as argument 5 converted
to frequency ratios in particular ranges. Instruments 1 and 2 accept continuous
pitchbend controls expressed in cents. Volume is only taken in consideration by
instruments 1 and 2.
The output score looks clumsy because of
the diverse argument formats used by instruments for this demo.
t 0.000 60.000
i1 0.000 0.250 4.05 30.000
34.850 0.000 -10.000 -4.500 0.000 ;F0
i1 0.000 0.250 4.05 30.000
34.850 0.000 -10.000 -4.500 0.000 ;F0
i2 0.750 0.250 5.05 6.499 11.999
44.550 49.400 0.000 0.000 0.000 ;F1
i3 0.750 0.100 643.50 1.005 ;D#6
i1 1.000 1.000 8.00 49.400
68.800 0.000 12.000 34.000 0.000 ;C4
i3 2.840 0.800 461.34 1.069 ;A5
i4 2.940 0.200 6.03 1.151 ;C2
i1 2.000 1.000 8.02 68.800
88.200 0.000 34.000 56.000 0.000 ;D4
i2 4.000 0.125 9.00 77.990
83.490 107.600 112.450 0.000 0.000 0.000 ;C5
i2 4.125 0.125 9.02 83.490
88.989 77.466 80.807 0.000 0.000 0.000 ;D5
i2 4.250 0.125 9.04 88.989
94.488 117.300 122.150 0.000 0.000 0.000 ;E5
s
Incidentally, this example shows that
BP2 does not necessarily produce a Csound score sorted on the on-setting dates
of events. This is not a limitation since Csound sorts out dates after reading
the score. BP2 does the same before compiling the Csound scores of its own
sound-object prototypes.
17.11 Combining argument values
Let us have a closer look at the Csound
score of sound-object prototype 'c'.
t 0 120
i2 0 0.2500 9.00 0 0 90 90 ; C5
i2 0.2500 0.2500 9.02 0 0 62 62
; D5
i2 0.500 0.2500 9.04 0 0 90 90 ;
E5
i2 0.7500 0.2500 9.05 0 0 90 90;
F5
e
The last two arguments represent volume.
Let p0 be the value in a particular place of a score line. (For instance, p0 =
62 on the second event.) If the volume is not explicitly controlled, then p0 is
copied to the output score. However, if a "_volume(x)" instruction
precedes the sound-object, the output value p1 is calculated as follows:
p1 = p0 * (x / default)
where 'default' is the default volume,
i.e. 90 in BP2.
For other controls such as pitchbend,
modulation, channel pressure and panoramic, a different formula is used:
p1 = p0 + x - default
where 'default' takes the following
values:
- 8191.5 for pitchbend
- 0 for channel pressure and modulation
- 64 for panoramic
These calculations are performed in the
MIDI parameter range. If the parameter is mapped to a different range in the
Csound domain, p0 is first converted to the MIDI range (using the reverse
mapping), the formula is applied, and then the result is mapped back to the
Csound range.
17.12 Tabulated functions
In § 17.10 we demonstrated
continuous changes of pitchbend and volume ranging over several sound-objects
and simple notes. Changes were simple in that their variations could be
described as two straight lines. Therefore the only useful information required
by the Csound instruments were the start and end values of each parameter.
The situation is often more complex.
Parameters may change following arbitrary definitions between the on-setting and
the off-setting of a Csound event (a line of the score). BP2 handles this case
automatically and builds a function table tied to the event which it inserts
before the score line.
In "-da.tryCsound",
try for instance:
_ins(1) _pitchrange(200)
_pitchbend(0) _pitchcont C4 _ _pitchbend(20)_ _ _pitchbend(165) _ _ D4 _ _ _
_pitchbend(150)
which yields the Csound score:
t 0.000 60.000
f101 0.000 256 -7
0.000 85
20.000 85
165.000 171
160.000
i1 0.000 6.000 8.00 90.000
90.000 0.000
0.000 160.000 101.000
; C4
i1 6.000 4.000 8.02 90.000
90.000 0.000
160.000 150.000
0.000 ; D4
s
Here the variation of pitchbend on 'D4'
is simple and requires only the start/end values (bold on the score). However,
the pitchbend variation on 'C4' requires four values: 0, 20, 165 and 160, which
BP2 stores in the 'f101' function table linked to 'C4'. The table index '101'
appears as the last argument in event 'C4'. When it is 0 (the case with 'D4')
no function table is attached.
In "-da.tryCsoundInstruments" a few examples demonstrate BP2's ability to combine
calculated parameter values with predefined ones contained in the Csound score
of a sound-object. See for instance a complex variation of 'blurb' on
sound-object 'e' which contains 4 lines of Csound score.
_cont(blurb) _value(blurb,12) e
_value(blurb,110) _ _value(blurb,130) _ _ _value(blurb,80) _ _
_value(blurb,-20) _ _value(blurb,-10) _ _ _ _value(blurb,40)
t 0.000 60.000
f101 0.000 256 -7 12.000 76
110.000 76 130.000 180 96.750
i2 0.000 3.330 7.04 8191.500
8191.500 64.000 64.000 12.000 96.750 101.000 ; E3
f102 0.000 256 -7 12.000 51
110.000 51 130.000 102 80.000 154 30.000
i2 0.000 5.000 7.00 8191.500
8191.500 64.000 64.000 12.000 30.000 102.000 ; C3
f103 5.000 256 -7
40.000 51 -6.000 51 8.000 205
70.000 ; table shifted
i2 5.000 5.000 7.02 8191.500
8191.500 64.000 64.000
40.000 70.000
103.000 ; D3
f104 6.660 256 -7 -13.400 26
-10.000 230 39.917
i2 6.660 3.335 7.07 8191.500
8191.500 64.000 64.000 -13.400 39.917 104.000 ; G3
s
BP2 created function tables attached to
each event. But there is more than that. In the Csound score of 'e', event 'D3'
had non-zero initial values on arguments 9 and 10. These values have been added
to the ones determined by variations of the 'blurb' parameter, thus yielding 40
for argument 9 (the start value of 'blurb') and 70 for argument 10 (the end
value). The same modification is reported in table 'f103', and all values in
the table changed accordingly.
The first and last values of a function
table always reflect the start and end values of the parameter it describes
variations of. This allows Csound instruments to operate consistently, either
interpolating start and end values, or looking at the attached function table.
17.13 Function tables in sound-object scores
The current version of BP2 does not
accept function tables in sound-object scores. This feature will be developed
shortly. Function tables in sound-objects should be combined with the ones
created by parameter variations in the performance.
17.14 A diagram of the cooperation between BP2 and Csound
Fig.38 BP2 and Csound: two complimentary environments...
