---
title: vDSP_deq22
framework: Kernel
role: symbol
role_heading: Function
platforms: [macOS 10.4+]
path: kernel/1532225-vdsp_deq22
---

# vDSP_deq22

Performs two-pole, two-zero recursive filtering on a single-precision vector.

## Declaration

```occ
void vDSP_deq22(const float *__A, vDSP_Stride __IA, const float *__B, float *__C, vDSP_Stride __IC, vDSP_Length __N);
```

## Parameters

- `__A`: The single-precision real input vector.
- `__IA`: The stride for input vector A.
- `__B`: Five single-precision input filter coefficients, with a stride of one.
- `__C`: The single-precision real output vector.
- `__IC`: The stride for output vector C.
- `__N`: The number of new output elements to produce.

## Discussion

Discussion This function creates N new values in output vector C, beginning at the third element. The function performs two-pole, two-zero recursive filtering on input vector A, which must contain at least N + 2 values; C must also contain at least N + 2 values.  Since the computation is recursive, prior to calling this function, initialize the first two elements in C.  You can only implement this function out of place — that is, the input and output memory must not overlap. This function performs the following operation: or (n = 2; n < N+2; ++n)      C[n] =         + A[n-0]*B[0]         + A[n-1]*B[1]         + A[n-2]*B[2]         - C[n-1]*B[3]         - C[n-2]*B[4];