Programmer Guide/Command Reference/EVAL/hth

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	1
0	hearing threshold in dB		w[i] = 1
1	hanning	not used	whanning(x{,scale})	w[i] = 0.5 - 0.5 * cos( a*i ) with: a = 2 * pi / (n-1)
2	hamming	not used	whamming(x{,scale})	w[i] = 0.54 - 0.46 * cos( a*i ) with: a = 2 * pi / (n-1)
3	blackman	0<par<=0.25 default=0.16	wblackman(x{,scale{,par}})	w[i] = (1-par)/2 - 0.5 * cos( a*i ) + par/2 * cos( 2*a*i ) with: a = 2 * pi / (n-1)
4	kaiser	0<par default=8	wkaiser(x{,scale{,par}})	w[i] = I0( par / m * sqrt(m^2 - (i-m)^2) ) / I0( par ) with: m = (n-1) / 2 I0(z) is the modfied zero-order bessel function
5	bartlett (triangle)	not used	wbartlett(x{,scale})	0 <= i <= m: w[i] = i / m m < i < n: w[i] = 2 - i / m with: m = (n-1) / 2
6	tappered rectangle	not used	wtaprect(x{,scale})	A rectangle with to short hanning slopes.
7	nuttall	not used	wnuttall(x{,scale})	A 4-term blackman-harris window with high dynamic range, low frequency resolution and minimized maximum sidelobes. Nuttall, Albert H. "Some Windows with Very Good Sidelobe Behavior." IEEE Transactions on Acoustics, Speech, and Signal Processing. Vol. ASSP-29 (February 1981). pp. 84-91
8	flat-top	not used	wflattop(x{,scale})	A 5-term blackman-harris window with high dynamic range, low frequency resolution and minimized passband ripple (< 0.01dB). Flat-top windows are primarily used for calibration purposes.
9	gauss	0<par<= 20 default=3	wgauss(x{,scale{,par}})	w[i] = exp( -0.5 * (par * (m - i) / m) ^ 2 ) with: m = (n-1) / 2

Notes:

• If the argument type has an invalid value, the rectangle window is used.
• If the energy-correction is enabled (argument scale!=0), the values w[i] scaled by a factor that approximately equalises the energy loss caused by the window function. The scaling factor is computed using white noise as test signal.
• If the argument par is supplied to a function not using this argument, it is ignored.

Result

The result r depends on the argument x:

• x is a number: The value is used as window length n. The result r is vector with length n containing the window function.
• x is a vector or matrix: The number of rows of x is used as window length. Each column of x is multiplied with the window function (element-wise) and stored in a column of r. The result r has the same type as x.

See also

fft, hth, wconvert

<function list>

hth

Hearing Threshold Level (HTH) or A/C spectral weightings.

Usage:

hth(f, type)

f

The frequency (scalar, vector or matrix).

type

The type of weighting function. The following values are supported:

0 - Hearing threshold level

1 - Hearing threshold weighting factor

2 - A weighting levels.

3 - A weighting factors.

4 - C weighting levels.

5 - C weighting factors.

Notes:

Factor = 1 / (10^(Level/20))

Result:

The result of the requested function (same datatype as f).