hth
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Compute spectral weights.
- Usage
hth(f, type)- f
- A scalar, vector or matrix containing the frequency value(s) in Hz.
- type
- The type of the spectral weight to be computed.
- Result
- The result w has the same type as the argument f and contains the values of the spectral weighting function selected by type (w[i,j] = weight(f[i,j],type)).
type description result 0 hearing threshold in dB LTH 1 hearing threshold weighting factor 10^(-LTH / 20) 2 value of the A weighting function in dB LA 3 A weighting factor 10^(-LA / 20) 4 value of the C weighting function in dB LC 5 C weighting factor 10^(-LC / 20)
- For LTH the algorithm published by E.Terhardt (JASA 71(3), March 1982) is used:
LTH(f) = 3.64 * f^-0.8 - 6.5 * exp(-0.6 * (f - 3.3)^2) + 1e-3 * f^4with: LTH = hearing threshold in dB, f = frequency in kHz
Example:
// compute the amplitude spectrum $#spe (in dBA) of the signal $#sig (fs=44.1kHz) // method 1: // a) compute linear amplitde spectrum of signal $#sig #spe := eval cr2len( fft( whanning( $#sig ) ) // b) compute the frequecies of the spectral bins #frq := eval fill( $#spe[] , 0 , 44100 / 2 / ( $#spe[]-1 ) ) // c) apply A-weights and convert to log. amplitudes $#spe := eval lin2log( $#spe ?* hth( $#frq , 3 ) ) // method 2: all-in-one #n := int npow2($#sig) #spe := eval lin2log(cr2len(fft(whanning($#sig)))) - hth(fill($#n/2+1,0,44100/$#n),2)
