mot566_interp (Motorola DSP Developer's Kit)

Upsample and filter an input signal.

MATLAB Syntax

Y = mot566_interp(X,R,N)
Y = mot566_interp(X,R,L,ALPHA)
[Y,B] = mot566_interp(X,R,L,ALPHA)

Description

mot566_interp(X,R) resamples the sequence in vector X at R times the original sample rate. The resulting resampled vector X is R times longer, mot566_length(Y) = R*mot566_length(X).

A symmetric filter, B, allows the original data to pass through unchanged and interpolates between so that the mean square error between them and their ideal values is minimized.

mot566_interp(X,R,L,ALPHA) allows specification of arguments L and ALPHA which otherwise default to 0.4 and 0.5 respectively. 2*L is the number of original sample values used to perform the interpolation. Ideally L should be less than or equal to 10. The length of B is 2*L*R+1. The signal is assumed to be band limited with cutoff frequency 0 < ALPHA<= 1.0.

[Y,B] = mot566_interp(X,R,L,ALPHA) returns the coefficients of the interpolation filter B.

Characteristics

In the workspace, if the input is:

X=[0.5641    0.4093    0.7053    0.6748    0.7565    0.4412    
0.5435] 
Alpha=0.34
R=2
L=3
[Y,B]=mot566_interp(X,R,L,Alpha)

the returned value is:

Y=[0.5641   0.4514   0.4093   0.5476   0.7053   0.7076   0.6748
   0.7392   0.7565   0.5978   0.4412   0.4552   0.5435   0.5966
B= -0.0000
    0.0162
         0
   -0.1095
    0.0000
    0.5934
    1.0000
    0.5934
    0.0000
   -0.1095
         0
    0.0162
   -0.0000

Arguments
X
Vector (or matrix) with elements normalized in the range [-1,1] (for complex elements, both real and imaginary parts should comply with this limit). Length of X should remain larger than two times L+1

Interpolation factor (integer) by which to increase the sample rate of the input sequence.

ALPHA
Cutoff frequency, normalized in [0,1].

L
Half the number of elements involved in interpolating.

Y
Interpolation result.

B
Coefficients of the interpolation filter.

See Also
mot566_decimate

mot566_ifft mot566_length