hd = double(h) returns a new filter hd that has the same structure and coefficients as h, but whose arithmetic property is set to double to use double-precision arithmetic for filtering. double(h) is not the same as the reffilter(h) function:

hd, the filter returned by double has the quantized coefficients of h represented in double-precision floating-point format
The reference filter returned by reffilter has double-precision, floating-point coefficients that have not been quantized.

You might find double(h) useful to isolate the effects of quantizing the coefficients of a filter by using double to create a filter hd that operates in double-precision but uses the quantized filter coefficients.

Examples

Use the same filter, once with fixed-point arithmetic and once with floating-point, to compare fixed-point filtering with double-precision floating-point filtering.

h = dfilt.dffir(firgr(27,[0 .4 .6 1],... 
[1 1 0 0]));              % Lowpass filter.
% Set h to use fixed-point arithmetic to filter.
% Quantize the coeffs.
h.arithmetic = 'fixed'; 
hd = double(h);           % Cast h to double-precision 
                          % floating-point coefficients.
n = 0:99; x = sin(0.7*pi*n(:)); % Set up an input signal.
y = filter(h,x);                % Fixed-point output.
yd = filter(hd,x);              % Floating-point output.
norm(yd-double(y),inf)
ans =

  9.2014e-004

norm shows that the largest difference (maximum error) between the output values from the fixed versus floating filtering comparison is about 0.0009 — either good or less good depending on your application.

double - Cast fixed-point filter to use double-precision arithmetic

Syntax

Description

Examples

See Also