Frequency response of filter
[h,w] = freqz(sysobj)
[h,w] = freqz(sysobj,n)
[h,w] = freqz(sysobj,'Arithmetic',arithType)
returns the complex frequency response
h of the filter
sysobj. The vector
the frequencies (in radians/sample) at which the function evaluates the frequency
response. The frequency response is evaluated at 8192 points equally spaced around
the upper half of the unit circle.
freqz uses the transfer function associated with the filter
to calculate the frequency response of the filter with the current coefficient
This examples plot the frequency response of the lowpass FIR filter using
b = fir1(80,0.5,kaiser(81,8)); firFilt = dsp.FIRFilter('Numerator',b); freqz(firFilt);
sysobj— Input filter
Input filter, specified as as one of the following filter System objects:
n— Number of points over which the frequency response is computed
Number of points over which the frequency response is computed. For an FIR
n is a power of two, the computation is done
faster using FFTs.
arithType— Arithmetic type
Specify the arithmetic used during analysis. When you specify
'single', the function
performs double- or single-precision analysis. When you specify
'fixed' , the arithmetic changes depending on the
setting of the
CoefficientDataType property and whether
object is locked or unlocked.
Details for Fixed-Point Arithmetic
|System Object State||Coefficient Data Type||Rule|
|Unlocked||The function assumes that the coefficient data type is signed, 16 bit, and autoscaled. The function performs fixed-point analysis based on this assumption.|
|Unlocked||The function performs fixed-point analysis based on the
setting of the
|Locked||When the input data type is |
|Locked||The function performs fixed-point analysis based on the
setting of the
When you do not specify the arithmetic for non-CIC structures, the function uses double-precision arithmetic if the filter System object is in an unlocked state. If the System object is locked, the function performs analysis based on the locked input data type. CIC structures only support fixed-point arithmetic.
h— Frequency response
n-element frequency response vector. If
n is not specified, the function uses a default
value of 8192. The frequency response is evaluated at
points equally spaced around the upper half of the unit circle.
Frequency vector of length
n, in radians/sample.
w consists of
n points equally
spaced around the upper half of the unit circle (from 0 to
π radians/sample). If
n is not
specified, the function uses a default value of 8192.
There are several ways of analyzing the frequency response of filters.
freqz accounts for quantization effects in the filter
coefficients, but does not account for quantization effects in filtering arithmetic. To
account for the quantization effects in filtering arithmetic, refer to function
freqz calculates the frequency response for a filter from the
filter transfer function Hq(z). The complex-valued
frequency response is calculated by evaluating
at discrete values of w specified by the syntax you use. The integer
n determines the number of equally-spaced points
around the upper half of the unit circle at which
the frequency response. The frequency ranges from 0 to π radians per sample when you do
not supply a sampling frequency as an input argument. When you supply the scalar
fs as an input argument to
freqz, the frequency ranges from 0 to