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fir_filters.go
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/
fir_filters.go
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package control
import (
"math"
"github.com/pkg/errors"
)
type movingAverageFilter struct {
filterSize int
smpCount int
x []float64
accumulator float64
}
func (f *movingAverageFilter) filterSample(x float64) float64 {
if f.smpCount < f.filterSize-1 {
f.smpCount++
f.accumulator += x
f.x[f.smpCount] = x
if f.smpCount == f.filterSize-1 {
f.accumulator /= float64(f.smpCount)
return f.accumulator
}
return 0.0
}
f.accumulator += (x - f.x[0]) / float64(f.smpCount)
f.x = f.x[1:]
f.x = append(f.x, x)
return f.accumulator
}
func (f *movingAverageFilter) Reset() error {
f.smpCount = 0
f.x = make([]float64, f.filterSize)
f.accumulator = 0.0
return nil
}
func (f *movingAverageFilter) Next(x float64) (float64, bool) {
y := f.filterSample(x)
return y, !math.IsNaN(y)
}
type firSinc struct {
smpFreq float64
cutOffFreq float64
order int
coeffs []float64
x []float64
}
func (f *firSinc) calculateCoefficients() error {
wc := 2.0 * f.cutOffFreq / f.smpFreq
n1 := (0.5) * (float64(f.order) - 1)
for i := 0; i < f.order; i++ {
if float64(i)-n1 == 0 {
f.coeffs[i] = wc
} else {
f.coeffs[i] = math.Sin(wc*math.Pi*(float64(i)-n1)) / (math.Pi * (float64(i) - n1))
}
}
return nil
}
func (f *firSinc) Reset() error {
f.coeffs = make([]float64, f.order)
f.x = make([]float64, f.order)
return f.calculateCoefficients()
}
func (f *firSinc) Next(x float64) (float64, bool) {
y := x * f.coeffs[0]
for i := 1; i < f.order; i++ {
y += f.x[i] * f.coeffs[f.order-i-1]
}
f.x = append(f.x, x)
f.x = f.x[1:]
return y, true
}
type firWindowedSinc struct {
smpFreq float64
cutOffFreq float64
kernelSize int
kernel []float64
x []float64
}
func (f *firWindowedSinc) Reset() error {
f.x = make([]float64, 0)
return f.calculateKernel()
}
func (f *firWindowedSinc) Next(x float64) (float64, bool) {
y := f.filterVal(x)
if math.IsNaN(y) {
return 0.0, false
}
return y, true
}
func (f *firWindowedSinc) calculateKernel() error {
wc := 2.0 * f.cutOffFreq / f.smpFreq
if wc > 1.0 {
return errors.New("ratio 2 * cutOffFreq/smpFreq cannot be below 1 (Nyquist frequency)")
}
f.kernel = make([]float64, f.kernelSize)
hs := f.kernelSize / 2
acc := 0.0
for i := 0; i < f.kernelSize; i++ {
if i-hs == 0 {
f.kernel[i] = math.Pi * wc
} else {
f.kernel[i] = math.Sin(math.Pi*wc*(float64(i-hs))) / float64(i-hs)
}
f.kernel[i] *= (0.54 - 0.46*math.Cos(math.Pi*float64(i/f.kernelSize)))
acc += f.kernel[i]
}
for i := 0; i < f.kernelSize; i++ {
f.kernel[i] /= acc
}
return nil
}
func (f *firWindowedSinc) filterVal(x float64) float64 {
if len(f.x) < f.kernelSize {
f.x = append(f.x, x)
return math.NaN()
}
y := 0.0
for i := 0; i < f.kernelSize; i++ {
y += f.kernel[i] * f.x[f.kernelSize-i-1]
}
f.x = append(f.x, x)
f.x = f.x[1:]
return y
}