Include Files

Domain Dependencies

Headers:

ippcore.h

,

ippvm.h

Libraries:

ippcore.lib

,

ippvm.lib

Description

The function

ippsResamplePolyphaseInit

initializes structures for data resampling using the ideal lowpass filter. The function

ippsResamplePolyphaseInit

applies the Kaiser window with alpha parameter and window width to the lowpass filter. This means that the values of the ideal lowpass filtering function are calculated for all

i

values such that |

i

/

nStep

|≤

window

.

Use the

pSpec

structure to resample input samples with the

ippsResample

function with arbitrary resampling factor. In this case, filter coefficients for each output sample are calculated using linear interpolation between two nearest values. The size of the filter depends on the resampling factor.

The function

ippsResamplePolyphaseFixedInit

initializes structures for data resampling with the factor equal to

inRate

/

outRate

. If you denote the number of filters created in the

IppsResamplingPolyphaseStructure

structure for input and output frequencies by

fnum

, then

fnum

=

outRate

/

GCD (

inRate

,

outRate

)

where

GCD (a, b)

is the greatest common divisor of

a

and

b

. For example, if

inRate

= 8000 and

outRate

= 11025, then the number of filters will be

fnum

= 11025/

GCD

(8000, 11025) = 441.

Functions with the

Fixed

suffix pre-calculate filter coefficients for each phase and store them in the data structure for better performance. Use these functions when the ratio

inRate

/

outRate

is rational only. These functions can be considerably faster but may require large data structures for some input and output rates.

Before calling these functions, you need to allocate memory for the resampling state structure. To calculate the memory size, filter length, and the number of filters, use the

ippsResamplePolyphaseGetSize

or

ippsResamplePolyphaseFixedGetSize

functions.