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Guitar feedback

References : Posted by Sean Costello

Notes :
It is fairly simple to simulate guitar feedback with a simple Karplus-Strong algorithm (this was described in a CMJ article in the early 90's):

Code :
Run the output of the Karplus-Strong delay lines into a nonlinear shaping function for distortion (i.e. 6 parallel delay lines for 6 strings, going into 1 nonlinear shaping function that simulates an overdriven amplifier, fuzzbox, etc.);

Run part of the output into a delay line, to simulate the distance from the amplifier to the "strings";

The delay line feeds back into the Karplus-Strong delay lines. By controlling the amount of the output fed into the delay line, and the length of the delay line, you can control the intensity and pitch of the feedback note.


Added on : 23/11/02 by ignatz[ AT ]webmail[ DOT ]co[ DOT ]za
Comment :
any C snippet code ???


Added on : 09/06/04 by lavirosa21[ AT ]aol[ DOT ]com
Comment :
              Are you Sean Costello the Blues Musician/Guitarist?


Added on : 22/08/04 by hagenkaiser[ AT ]gmx[ DOT ]de
Comment :
              what is a Karplus-Strong-Delay??

Added on : 25/10/04 by brainslayer[ AT ]braincontrol[ DOT ]org
Comment :
a physical modelling algorithm

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Added on : 10/06/16 by jorge2017a1[ AT ]gmail[ DOT ]com
Comment :
              formula.......... y (n) =  x(n) + c * [ y (n-N) + y (n - (N+1))]
'''A simple model (based on Karplus-Strong algorithm) may be used to model a plucked string instrument like a guitar.
'''The input-output relationship of the causal LTI system is given by:
'''    y (n) =  x(n) + ? * [ y (n-N) + y (n - (N+1))]
'''    x(n) is a zero mean random variable, uniformly distributed between -1 and 1
'''    y(n) is the output
'''c is a real-valued constant, whose typical value is 0.5 (experiment with other values and comment)
'''N controls the pitch of the note; N = floor ( Fs / Fp), where Fs is the sampling frequency in Hz, and Fp
'''is the pitch of the note in Hz.  For example, at 8 kHz sampling frequency, N = 20 implies a pitch frequency of 400 Hz.

Added on : 10/06/16 by jorge2017a1[ AT ]gmail[ DOT ]com
Comment :
'NO esta completo falta algo, no se, si es el filtro biquad

Public Function karplustrong_b1(PNumSamples As Long) As Integer()
Dim x() As Single
Dim y() As Single
Dim n As Long
Dim Num As Long
Dim ArrResp() As Integer
Dim C As Single
Dim Fs As Long
Dim fP As Single
Dim amplitud As Long
Dim i As Long
Dim valor As Single
Dim Ind1 As Long
Dim Ind2 As Long
Dim suma As Single
Dim media As Single
Dim valorsigno As Single

    Fs = 44100
    fP = 400 '400hz pitch frequency
    'Num = (Fs / Fp)

    ReDim x(PNumSamples)
    ReDim y(PNumSamples)
    'generar numeros aleatorios rango 0 a 1
    'iniciar numeros aleatorios
    suma = 0
    For i = 0 To PNumSamples
        valor = Rnd * 1 - 0.5
        'valorsigno = Rnd * 1
        'If valorsigno > 0.5 Then valor = -valor
        x(i) = valor
        suma = suma + valor
    media = suma / PNumSamples
    'media = 1
    'calcular la media y dividir
    For i = 0 To PNumSamples
        valor = x(i)
        x(i) = valor / media
    Num = PNumSamples - 1
    C = 0.5
    For n = 0 To PNumSamples - 1
        'Ind1 = Abs(n - Num)
        'Ind2 = Abs(n - (Num + 1))
        Ind2 = Abs((n))
        Ind2 = Abs((n + 1) Mod Num) / 2
        y(n) = x(n) + C * (y(Ind1) + y(Ind2))

    ReDim ArrResp(PNumSamples)
    amplitud = 1000
    For i = 0 To Num
        ArrResp(i) = RangoInteger(y(i) * amplitud)
    karplustrong_b1 = ArrResp
End Function

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