24. rand, buzz and gbuzz

rand, buzz and gbuzz are three opcodes producing frequency rich signals. They usually have to be filtered to remove frequencies, a topic covered later.

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The rand opcode generates a random sequence. All the random values are between minus and positive of the first parameter, and the only required one.

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This String uses a rand opcode, to generate a sequence between negative .5 and positive .5.

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A noise signal will have a nearly uniform frequency spectrum.

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The buzz opcode uses a sine input frequency, to create a signal with many harmonics. In xcps we give the fundamental frequency, and then we give the number of harmonics we need.

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In this String using the buzz opcode, we request 3 harmonics of 440 Hz. The parameter value 1 indicates the table where the sine function is located, for our example.

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In the frequency spectrum, we can see that there are three frequencies, 440 Hz, 2 times 440 Hz, and 3 times 440 Hz. All three have the same magnitude.

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The gbuzz opcode creates a set of harmonics based on a cosine wave. We have to give it the fundamental frequency, number of harmonics in the output and the lowest harmonic that will be in the output. In addition, there is a parameter, kmul, which is a multiplying factor, controlling how harmonics increase or decrease.

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This Instrument String, uses gbuzz to create 3 harmonics of 440 Hz, but we start with the 2nd harmonic (2 times 440 Hz) and the higher frequencies damp off with a multiplying factor of 0.7. We use the cosine table, which is numbered 2, in our program.

# Main.py

from moduleCsound import *
addTag(startSyn,startOpt,stopOpt,startIns)
header()

# *** Instrument Strings ***

randStr="""
asig rand 0.5
out asig
"""

buzzStr="""
asig buzz 1, 440, 3, 1
out asig 
"""

gbuzzStr="""
asig gbuzz 1, 440, 3, 2, 0.7, 2
out asig
"""


instrument('rand',1,randStr)
instrument('buzz',2,buzzStr)
instrument('gbuzz',3,gbuzzStr)

addTag(stopIns,startSco)

# *** Table ***
table('1. Sine wave',1,0,8192,10,1)
table('2. Cosine wave',2,0,8192,11,1,1)

# *** Score ***
score(1,0,3)
score(2,3,3)
score(3,6,3)

addTag(stopSco,stopSyn)
writeRun('Tut24')

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This shows the three frequencies starting at 880 Hz (2 times 440 Hz) which are reducing at the rate of 0.7.

; Tut24.csd
<CsoundSynthesizer>
<CsOptions>
</CsOptions>
<CsInstruments>
sr = 44100
ksmps = 10
nchnls = 1
0dbfs = 1
; rand
instr 1
  asig rand 0.5
  out asig
endin
; buzz
instr 2
  asig buzz 1, 440, 3, 1
  out asig 
endin
; gbuzz
instr 3
  asig gbuzz 1, 440, 3, 2, 0.7, 2
  out asig
endin
</CsInstruments>
<CsScore>
; 1. Sine wave
f 1 0 8192 10 1
; 2. Cosine wave
f 2 0 8192 11 1 1
i 1 0 3
i 2 3 3
i 3 6 3
</CsScore>
</CsoundSynthesizer>

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You will find additional information at pythonaudio.blogspot.com, including the source code.

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This is the video of Tutorial 24: