Csound.

1
Csound.

• a language for describing sound

2
General History.

• Developed by Barry Vercoe at MIT.
• Extended by too many people to mention.
• Based initially on work done by Vercoe and Max
  Matthews for creating music on IBM 7094 and 360
  machines.
• These first programs were written in assembler,
  and CSound has retained the overall flavor of
  assembler code in its style.
• The name CSound comes from the rendterpreter
  being implemented in the C programming language.

3
Rendterpreter?

• CSound source files are interpreted, then
  rendered.
• The language utilizes variables and function
  definitions that can only be evaluated at
  runtime, and also allows real-time interaction
  through MIDI thus it is interpreted.
• However, the output of CSound source files is
  always sound after variables and functions are
  bound, the source is carried to an intermediate
  form, from which it is written into pulse code
  modulation audio data (either directly to a file
  or into system-specific audio API)

4
General Structure

• Every CSound program can be broken down into the
  orchestra file and the score file.
• by convention, these use .orc and .sco extensions
• the orchestra file contains all the instruments
  the score file contains how and when to play
  them.
• Each file type has a fairly well-defined
  structure using opcode-type primitives and
  methods.
• For example, the orchestra header ALWAYS begins
  with something of the form

sr gt sampling rate for audio kr gt control
rate ksmps gt sr / kr nchlns gt number of audio
channels
sr 44100 kr 4410 ksmps
10 nchnls 2
5
Opcodes.

• CSound modules, or opcodes, are just like
  assembler opcodes a base function with
  white-space delimited arguments.

e.g.
foscil 10000 440 1 1.5 8 1

• CSound also uses GEN functions to create
  datatables for opcodes these routines generate
  everything from simple sines/cosines to
  Blackman-Harris windows, used in spectrum analysis

generates a Hanning window of with max value 1.
e.g.
f3 0 4097 20 2 1
6
Binding, Scoping, Parameters, Oh my...

• Binding is really irrelevant in Csound there are
  no procedures
• Scoping variables can be scoped either
• within a single instrument
• An instrument has a block structure
• instr 107
• a1 oscil p4, p5, p6
• out a1
• endin
• within a score/orchestra file combination
  (referred to as global)
• All parameters are passed by value the
  mechanism is by simply placing a numeric value or
  variable name in the appropriate p-field
  (analogous to a register argument in assembler),
  e.g. p4 through p6 above.
• All variables in CSound must begin with one of
  the letters a, d, k, i, w, x, or z. (making them
  feel even more like registers....)

7
So why the hell would anyone want to go to all
that trouble?

• Its free.
• Its limitless in terms of the noises one can
  make.
• Its available for almost every platform.
• Many, many development environments are available
  (e.g., integration into MAX/MSP)
• Online documentation is exhaustive (think the
  Java API on the Sun site)
• The language has had excellent longevity and
  keeps getting better, with a richer set of
  built-in features and opcodes.
• Highly efficient speed is directly related to
  complexity.

8
However...

• Code is not very readable / maintainable compared
  to most real programming languages (its a lot
  less like spoken English)
• The learning curve is pretty steep
• Its control flow is fairly limited conditionals
  have to be implemented in a manner somewhat akin
  to gates on a circuit
• Aside from blatant syntax errors, debugging
  messages occur entirely between ears and brain.

9
A small example.
me999.orc simple buzz instrument sr
44100 kr 4410 ksmps
10 nchnls 1 instr 109 a1
buzz p4, p5, p6, p7 out a1
endin
10
A small example, cont.
me999.sco score for buzz instrument FUNCTION
1 USES THE GEN10 SUBROUTINE TO COMPUTE A SINE
WAVE FUNCTION 2 USES THE GEN10 SUBROUTINE BUT
SPECIFIES AMPLITUDES OF THE FIRST 12 PARTIALS f1
0 4096 10 1 f2 0 4096 10 1 .5 .323 .25
.3 .189 .142 .125 .111 .1 .09 .107 bass i109 0 0
.97 1600 440 25 1 i109 1 1 1600 330 22 1 i109 2 1
1600 256 20 1 i109 3 1 1600 329.6 18 1 alto i109
0 0.2 1600 1245 10 1 i109 0.2 0.2 1600 627 8 1 i1
09 0.4 0.2 1600 568 5 1 i109 0.6 0.2 1600 660 7 1
i109 0.8 0.2 1600 1245 5 1 i109 1 0.2 1600 1345 10
1 i109 1.2 0.2 1600 727 8 1 i109 1.4 0.2 1600 668
5 1 i109 1.6 0.2 1600 660 7 1 i109 1.8 0.2 1600 1
245 5 1 . . .
11
Demos and Resources

• me999.orc and me999.sco render to
• me999.wav
• A much bigger example
• shortyorc.txt and shortyscore.txt render to
  shorty.wav
• using a MIDI keyboard and controller
• ambientsong.mp3
• The Csound website www.csound.org
• The Online Csound Manual
• http//www.lakewoodsound.com/csound/hypertext/manu
  al.htm