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[Timo Beckman]

A bit of data on 3 processors

https://timobeckmangeluid.wordpress.com/2020/12/17/processors-interim-report-lake-lm26-vs-apex-intelli-x2-vs-linea-research-asc48/

[Timo Beckman]

Added a bunch of screen shots and the Smaart V8 TRF files for download 😉

[Chris Grimshaw]

Interesting post!

I'll have to do the maths and figure out which (if any!) of the processors had their Q-factors correct. I could probably measure my Powersoft T-series amps if that'd be of interest.

Chris

[Timo Beckman]

I have a Powersoft X8dante ready to be victimised ;-)

Might take some though

[Frank Koenig]

Interesting post!

I'll have to do the maths and figure out which (if any!) of the processors had their Q-factors correct. I could probably measure my Powersoft T-series amps if that'd be of interest.

Chris

I know it's irritating that there is no standard for this. For what it's worth, here's what I determined (empirically) for Powersoft's peaking filters. In the R function below f0 is the center frequency in Hz, AdB is the boost/cut amount in dB, Q is Q, N is the number of points, and deltaF is the sampling rate in Hz / N.

a[1], a[2], a[3], b[1], b[2], b[3] are the denominator and numerator coefficients of the transfer function, respectively, in terms of f0, AdB, and Q. Thankfully, Powersoft appears to take a straight forward approach to this. I like them.

#-----------------Bi-Quadratic peaking filter (Powersoft parameters)
biQuad <- function(f0, AdB, Q, N, deltaF){
  w <- 2 * pi * f0
  A <- 10^(AdB / 20)
  a <- numeric(3)
  b <- numeric(3)
  if (A >= 1){
    a[2] <-     w / (Q * 2)
    b[2] <- A * w / (Q * 2)
  }
  if (A < 1){
    a[2] <- w / (Q * 2) / A
    b[2] <- w / (Q * 2)
  }
  a[3] <- 1
  b[3] <- 1
  a[1] <- w^2
  b[1] <- w^2
  s <- complex(N, 0, 0:(N - 1) * 2 * pi * deltaF)
  (b[1] + b[2]*s + b[3]*s^2) / (a[1] + a[2]*s + a[3]*s^2)
}

--Frank

[Timo Beckman]

And now in normal (non-math) English? (Sorry ;-) )

I know it's irritating that there is no standard for this. For what it's worth, here's what I determined (empirically) for Powersoft's peaking filters. In the R function below f0 is the center frequency in Hz, AdB is the boost/cut amount in dB, Q is Q, N is the number of points, and deltaF is the sampling rate in Hz / N.

a[1], a[2], a[3], b[1], b[2], b[3] are the denominator and numerator coefficients of the transfer function, respectively, in terms of f0, AdB, and Q. Thankfully, Powersoft appears to take a straight forward approach to this. I like them.

#-----------------Bi-Quadratic peaking filter (Powersoft parameters)
biQuad <- function(f0, AdB, Q, N, deltaF){
  w <- 2 * pi * f0
  A <- 10^(AdB / 20)
  a <- numeric(3)
  b <- numeric(3)
  if (A >= 1){
    a[2] <-     w / (Q * 2)
    b[2] <- A * w / (Q * 2)
  }
  if (A < 1){
    a[2] <- w / (Q * 2) / A
    b[2] <- w / (Q * 2)
  }
  a[3] <- 1
  b[3] <- 1
  a[1] <- w^2
  b[1] <- w^2
  s <- complex(N, 0, 0:(N - 1) * 2 * pi * deltaF)
  (b[1] + b[2]*s + b[3]*s^2) / (a[1] + a[2]*s + a[3]*s^2)
}

--Frank

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