Overview
Interpolator combining an upsampler and an FIR filter
Discussion
The FIR interpolator module implements an upsampler (zero stuffer) followed by an FIR filter. An efficient polyphase algorithm is used which reduces the processing load. The module operates on multiple channels with all channels sharing the same set of filter coefficients. The filter coefficients are stored in the array coeffs in normal order. Each channel uses a circular buffer of length N/L, where N is the filter length and L is the interpolation factor.
The output block size equals the input block size multiplied by L. The output sample rate equals the input sample rate multiplied by L.
Type Definition
| Code Block |
|---|
typedef struct _ModuleFIRInterpolatorFract32
{
ModuleInstanceDescriptor instance; // Common Audio Weaver module instance structure
INT32 L; // Upsampling factor
INT32 N; // Length of the filter
INT32 postShift; // Number of bits to shift
INT32 polyphaseLen; // Length of each polyphase filter component
INT32 stateIndex; // Index of the oldest state variable in the array of state variables
INT32 stateLen; // Length of the circular state buffer
FLOAT32* coeffs; // Filter coefficient array in normal order
fract32* coeffsFract32; // Filter coefficient fract32 array in normal order
fract32* state; // State variable array. The size of the array equals stateLen * numChannels
} ModuleFIRInterpolatorFract32Class; |
Variables
Properties
Name | Type | Usage | isHidden | Default value | Range | Units |
L | int | const | 0 | 2 | 1:1:512 | |
N | int | const | 0 | 32 | 1:1:5000 | samples |
postShift | int | derived | 1 | 0 | Unrestricted | |
polyphaseLen | int | const | 1 | 16 | Unrestricted | |
stateIndex | int | state | 1 | 0 | Unrestricted | |
stateLen | int | const | 1 | 16 | Unrestricted | |
coeffs | float* | parameter | 0 | [32 x 1] | Unrestricted | |
coeffsFract32 | fract32* | derived | 0 | [34 x 1] | Unrestricted | |
state | fract32* | state | 1 | [16 x 1] | Unrestricted |
Pins
Input Pins
Name: in
Description: audio input
...
Sample rate range: Unrestricted
Complex support: Real
Output Pins
Name: out
Description: audio output
Data type: fract32
MATLAB Usage
File Name: fir_interpolator_fract32_module.m
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