Merged in audiofiltering (pull request #492)

Audiofiltering:

Implemented audiofilters. Lowpass, HIghpass, Bandpass, Bandstop, Amplifier.

Approved-by: Saxon Milton
Approved-by: Trek Hopton

codec/pcm/filters.go

@@ -0,0 +1,328 @@
+/*
+NAME
+  filters.go
+
+DESCRIPTION
+  filter.go contains functions for filtering PCM audio.
+
+AUTHOR
+  David Sutton <davidsutton@ausocean.org>
+
+LICENSE
+  filters_test.go is Copyright (C) 2023 the Australian Ocean Lab (AusOcean)
+
+  It is free software: you can redistribute it and/or modify them
+  under the terms of the GNU General Public License as published by the
+  Free Software Foundation, either version 3 of the License, or (at your
+  option) any later version.
+
+  It is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+  for more details.
+
+  You should have received a copy of the GNU General Public License in gpl.txt.
+  If not, see [GNU licenses](http://www.gnu.org/licenses).
+*/
+
+package pcm
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"math"
+
+	"github.com/mjibson/go-dsp/fft"
+	"github.com/mjibson/go-dsp/window"
+)
+
+// AudioFilter is an interface which contains an Apply function.
+// Apply is used to apply the filter to the given buffer of PCM data (b.Data).
+type AudioFilter interface {
+	Apply(b Buffer)
+}
+
+// SelectiveFrequencyFilter is a struct which contains all the filter specifications required for a
+// lowpass, highpass, bandpass, or bandstop filter.
+type SelectiveFrequencyFilter struct {
+	coeffs     []float64
+	cutoff     [2]float64
+	sampleRate uint
+	taps       int
+	buffInfo   BufferFormat
+}
+
+// NewLowPass populates a LowPass struct with the specified data. The function also
+// generates a lowpass filter based off the given specifications, and returns a pointer.
+func NewLowPass(fc float64, info BufferFormat, length int) (*SelectiveFrequencyFilter, error) {
+	return newLoHiFilter(fc, info, length, [2]float64{0, fc})
+}
+
+// NewHighPass populates a HighPass struct with the specified data. The function also
+// generates a highpass filter based off the given specifications, and returns a pointer.
+func NewHighPass(fc float64, info BufferFormat, length int) (*SelectiveFrequencyFilter, error) {
+	return newLoHiFilter(fc, info, length, [2]float64{fc, 0})
+}
+
+// NewBandPass populates a BandPass struct with the specified data. The function also
+// generates a bandpass filter based off the given specifications, and returns a pointer.
+func NewBandPass(fc_lower, fc_upper float64, info BufferFormat, length int) (*SelectiveFrequencyFilter, error) {
+	newFilter, lp, hp, err := newBandFilter([2]float64{fc_lower, fc_upper}, info, length)
+	if err != nil {
+		return nil, fmt.Errorf("could not create new band filter: %w", err)
+	}
+
+	// Convolve the filters to create a bandpass filter.
+	newFilter.coeffs, err = fastConvolve(hp.coeffs, lp.coeffs)
+	if err != nil {
+		return nil, fmt.Errorf("could not compute fast convolution: %w", err)
+	}
+
+	// Return a pointer to the filter.
+	return newFilter, nil
+}
+
+// NewBandStop populates a BandStop struct with the specified data. The function also
+// generates a bandstop filter based off the given specifications, and returns a pointer.
+func NewBandStop(fc_lower, fc_upper float64, info BufferFormat, length int) (*SelectiveFrequencyFilter, error) {
+	newFilter, lp, hp, err := newBandFilter([2]float64{fc_upper, fc_lower}, info, length)
+	if err != nil {
+		return nil, fmt.Errorf("could not create new band filter: %w", err)
+	}
+	size := newFilter.taps + 1
+	newFilter.coeffs = make([]float64, size)
+	for i := range lp.coeffs {
+		newFilter.coeffs[i] = lp.coeffs[i] + hp.coeffs[i]
+	}
+
+	// Return a pointer to the filter.
+	return newFilter, nil
+}
+
+// Apply is the SelectiveFrequencyFilter implementation of the AudioFilter interface. This implementation
+// takes the buffer data (b.Data), applies the highpass filter and returns a byte slice of filtered audio.
+func (filter *SelectiveFrequencyFilter) Apply(b Buffer) ([]byte, error) {
+	// Apply the lowpass filter to the given audio buffer.
+	return convolveFromBytes(b.Data, filter.coeffs)
+}
+
+// Amplifier is a struct which contains the factor of amplification to be used in the application
+// of the filter.
+type Amplifier struct {
+	factor float64
+}
+
+// NewAmplifier defines the factor of amplification for an amplifying filter.
+func NewAmplifier(factor float64) Amplifier {
+	// Return populated Amplifier filter.
+	// Uses the absolute value of the factor to ensure compatibility.
+	return Amplifier{factor: math.Abs(factor)}
+}
+
+// Apply implemented for an amplifier takes the buffer data (b.Data), applies
+// the amplification and returns a byte slice of filtered audio.
+func (amp *Amplifier) Apply(b Buffer) ([]byte, error) {
+	inputAsFloat, err := bytesToFloats(b.Data)
+	if err != nil {
+		return nil, fmt.Errorf("failed to convert to floats: %w", err)
+	}
+
+	// Multiply every sample by the factor of amplification.
+	floatOutput := make([]float64, len(inputAsFloat))
+	for i := range inputAsFloat {
+		floatOutput[i] = inputAsFloat[i] * amp.factor
+		// Stop audio artifacting by clipping outputs.
+		if floatOutput[i] > 1 {
+			floatOutput[i] = 1
+		} else if floatOutput[i] < -1 {
+			floatOutput[i] = -1
+		}
+	}
+	outBytes, err := floatsToBytes(floatOutput)
+	if err != nil {
+		return nil, fmt.Errorf("failed to convert to bytes: %w", err)
+	}
+	return outBytes, nil
+}
+
+// newLoHiFilter is a function which checks for the validity of the input parameters, and calls the newLoHiFilter function
+// to return a pointer to either a lowpass or a highpass filter.
+func newLoHiFilter(fc float64, info BufferFormat, length int, cutoff [2]float64) (*SelectiveFrequencyFilter, error) {
+	// Ensure that all input values are valid.
+	if fc <= 0 || fc >= float64(info.Rate)/2 {
+		return nil, errors.New("cutoff frequency out of bounds")
+	} else if length <= 0 {
+		return nil, errors.New("cannot create filter with length <= 0")
+	}
+
+	// Determine the type of filter to be generated.
+	var fd float64
+	var factor1 float64
+	var factor2 float64
+	if cutoff[0] == 0 { // For a lowpass filter, cutoff[0] = 0, cutoff[1] = fc.
+		// The filter must be a lowpass filter.
+		fd = cutoff[1] / float64(info.Rate)
+		factor1 = 1
+		factor2 = 2 * fd
+	} else if cutoff[1] == 0 { // For a highpass filter, cutoff[0] = fc, cutoff[1] = 0.
+		// The filter must be a highpass filter.
+		fd = cutoff[0] / float64(info.Rate)
+		factor1 = -1
+		factor2 = 1 - 2*fd
+	} else {
+		// Otherwise the filter must be a different type of filter.
+		return nil, errors.New("tried to use newLoHiFilter to generate bandpass or bandstop filter")
+	}
+
+	// Create a new filter struct to return, populated with all correct data.
+	var newFilter = SelectiveFrequencyFilter{cutoff: cutoff, sampleRate: info.Rate, taps: length, buffInfo: info}
+
+	// Create a filter with characteristics from struct.
+	size := newFilter.taps + 1
+	newFilter.coeffs = make([]float64, size)
+	b := 2 * math.Pi * fd
+	winData := window.FlatTop(size)
+	for n := 0; n < (newFilter.taps / 2); n++ {
+		c := float64(n) - float64(newFilter.taps)/2
+		y := math.Sin(c*b) / (math.Pi * c)
+		newFilter.coeffs[n] = factor1 * y * winData[n]
+		newFilter.coeffs[size-1-n] = newFilter.coeffs[n]
+	}
+	newFilter.coeffs[newFilter.taps/2] = factor2 * winData[newFilter.taps/2]
+
+	// Return a pointer to the filter.
+	return &newFilter, nil
+}
+
+// newBandFilter creates a ensures the validity of the input parameters, and generates appropriate lowpass and highpass filters
+// required for the creation of the specific band filter.
+func newBandFilter(cutoff [2]float64, info BufferFormat, length int) (new, lp, hp *SelectiveFrequencyFilter, err error) {
+	// Ensure that all input values are valid.
+	if cutoff[0] <= 0 || cutoff[0] >= float64(info.Rate)/2 {
+		return nil, nil, nil, errors.New("cutoff frequencies out of bounds")
+	} else if cutoff[1] <= 0 || cutoff[1] >= float64(info.Rate)/2 {
+		return nil, nil, nil, errors.New("cutoff frequencies out of bounds")
+	} else if length <= 0 {
+		return nil, nil, nil, errors.New("cannot create filter with length <= 0")
+	}
+	// Create a new filter struct to return, populated with all correct data.
+	// For a bandpass filter, cutoff[0] = fc_l, cutoff[1] = fc_u.
+	// For a bandstop filter, cutoff[0] = fc_u, cutoff[1] = fc_l.
+	var newFilter = SelectiveFrequencyFilter{cutoff: cutoff, sampleRate: info.Rate, taps: length, buffInfo: info}
+
+	// Generate lowpass and highpass filters to create bandpass filter with.
+	hp, err = NewHighPass(newFilter.cutoff[0], newFilter.buffInfo, newFilter.taps)
+	if err != nil {
+		return nil, nil, nil, fmt.Errorf("could not create new highpass filter: %w", err)
+	}
+	lp, err = NewLowPass(newFilter.cutoff[1], newFilter.buffInfo, newFilter.taps)
+	if err != nil {
+		return nil, nil, nil, fmt.Errorf("could not create new lowpass filter: %w", err)
+	}
+
+	// Return pointer to new filter.
+	return &newFilter, hp, lp, nil
+}
+
+// convolveFromBytes takes in a byte slice and a float64 slice for a filter, converts to floats,
+// convolves the two signals, and converts back to bytes and returns the convolution.
+func convolveFromBytes(b []byte, filter []float64) ([]byte, error) {
+	bufAsFloats, err := bytesToFloats(b)
+	if err != nil {
+		return nil, fmt.Errorf("could not convert to floats: %w", err)
+	}
+
+	// Convolve the floats with the filter.
+	convolution, err := fastConvolve(bufAsFloats, filter)
+	if err != nil {
+		return nil, fmt.Errorf("could not compute fast convolution: %w", err)
+	}
+	outBytes, err := floatsToBytes(convolution)
+	if err != nil {
+		return nil, fmt.Errorf("could not convert convolution to bytes: %w", err)
+	}
+	return outBytes, nil
+}
+
+func bytesToFloats(b []byte) ([]float64, error) {
+	// Ensure the validity of the input.
+	if len(b) == 0 {
+		return nil, errors.New("no audio to convert to floats")
+	} else if len(b)%2 != 0 {
+		return nil, errors.New("uneven number of bytes (not whole number of samples)")
+	}
+
+	// Convert bytes to floats.
+	inputAsFloat := make([]float64, len(b)/2)
+	inputAsInt := make([]int16, len(b)/2)
+	bReader := bytes.NewReader(b)
+	for i := range inputAsFloat {
+		binary.Read(bReader, binary.LittleEndian, &inputAsInt[i])
+		inputAsFloat[i] = float64(inputAsInt[i]) / (math.MaxInt16 + 1)
+	}
+	return inputAsFloat, nil
+}
+
+// floatsToBytes converts a slice of float64 PCM data into a slice of signed 16bit PCM data.
+// The input float slice should contains values between -1 and 1. The function converts these values
+// to a proportionate unsigned value between 0 and 65536. This 16bit integer is split into two bytes,
+// then returned in Little Endian notation in a byte slice double the length of the input.
+func floatsToBytes(f []float64) ([]byte, error) {
+	buf := new(bytes.Buffer)
+	bytes := make([]byte, len(f)*2)
+	for i := range f {
+		err := binary.Write(buf, binary.LittleEndian, int16(f[i]*math.MaxInt16))
+		if err != nil {
+			return nil, fmt.Errorf("failed to write ints as bytes: %w", err)
+		}
+	}
+	n, err := buf.Read(bytes)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read bytes from buffer: %w", err)
+	} else if n != len(bytes) {
+		return nil, fmt.Errorf("buffer and output length mismatch read %d bytes, expected %d: %w", n, len(bytes), err)
+	}
+
+	return bytes, nil
+}
+
+// fastConvolve takes in a signal and an FIR filter and computes the convolution (runs in O(nlog(n)) time).
+func fastConvolve(x, h []float64) ([]float64, error) {
+	// Ensure valid data to convolve.
+	if len(x) == 0 || len(h) == 0 {
+		return nil, errors.New("convolution requires slice of length > 0")
+	}
+
+	// Calculate the length of the linear convolution.
+	convLen := len(x) + len(h) - 1
+
+	// Pad signals to the next largest power of 2 larger than convLen.
+	padLen := int(math.Pow(2, math.Ceil(math.Log2(float64(convLen)))))
+	zeros := make([]float64, padLen-len(x), padLen-len(h))
+	x = append(x, zeros...)
+	zeros = make([]float64, padLen-len(h))
+	h = append(h, zeros...)
+
+	// Compute DFFTs.
+	x_fft, h_fft := fft.FFTReal(x), fft.FFTReal(h)
+
+	// Compute the multiplication of the two signals in the freq domain.
+	y_fft := make([]complex128, padLen)
+	for i := range x_fft {
+		y_fft[i] = x_fft[i] * h_fft[i]
+	}
+
+	// Compute the IDFFT.
+	iy := fft.IFFT(y_fft)
+
+	// Convert to []float64.
+	y := make([]float64, padLen)
+	for i := range iy {
+		y[i] = real(iy[i])
+	}
+
+	// Trim to length of linear convolution and return.
+	return y[0:convLen], nil
+}

codec/pcm/filters_test.go

@@ -0,0 +1,368 @@
+/*
+NAME
+  filters_test.go
+
+DESCRIPTION
+  filter_test.go contains functions for testing functions in filters.go.
+
+AUTHOR
+  David Sutton <davidsutton@ausocean.org>
+
+LICENSE
+  filters_test.go is Copyright (C) 2023 the Australian Ocean Lab (AusOcean)
+
+  It is free software: you can redistribute it and/or modify them
+  under the terms of the GNU General Public License as published by the
+  Free Software Foundation, either version 3 of the License, or (at your
+  option) any later version.
+
+  It is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+  for more details.
+
+  You should have received a copy of the GNU General Public License in gpl.txt.
+  If not, see [GNU licenses](http://www.gnu.org/licenses).
+*/
+
+package pcm
+
+import (
+	"math"
+	"math/cmplx"
+	"os"
+	"testing"
+
+	"github.com/mjibson/go-dsp/fft"
+)
+
+// Set constant values for testing.
+const (
+	sampleRate   = 44100
+	filterLength = 500
+	freqTest     = 1000
+)
+
+// TestLowPass is used to test the lowpass constructor and application. Testing is done by ensuring frequency response as well as
+// comparing against an expected audio file.
+func TestLowPass(t *testing.T) {
+	// Generate an audio buffer to run test on.
+	genAudio, err := generate()
+	if err != nil {
+		t.Fatal(err)
+	}
+	var buf = Buffer{Data: genAudio, Format: BufferFormat{SFormat: S16_LE, Rate: sampleRate, Channels: 1}}
+
+	// Create a lowpass filter to test.
+	const fc = 4500.0
+	lp, err := NewLowPass(fc, buf.Format, filterLength)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Filter the audio.
+	filteredAudio, err := lp.Apply(buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Take the FFT of the signal.
+	filteredFloats, err := bytesToFloats(filteredAudio)
+	if err != nil {
+		t.Fatal(err)
+	}
+	filteredFFT := fft.FFTReal(filteredFloats)
+
+	// Check if the lowpass filter worked (any high values in filteredFFT above cutoff freq result in fail).
+	for i := int(fc); i < sampleRate/2; i++ {
+		mag := math.Pow(cmplx.Abs(filteredFFT[i]), 2)
+		if mag > freqTest {
+			t.Error("Lowpass filter failed to meet spec.")
+			break
+		}
+	}
+
+	// Read audio from the test location.
+	const fileName = "../../../test/test-data/av/input/lp_4500.pcm"
+	expectedAudio, err := os.ReadFile(fileName)
+	if err != nil {
+		t.Fatalf("File for comparison not read.\n\t%s", err)
+	}
+
+	// Compare the filtered audio against the expected signal.
+	compare(filteredAudio, expectedAudio, t)
+}
+
+// TestHighPass is used to test the highpass constructor and application. Testing is done by ensuring frequency response as well as
+// comparing against an expected audio file.
+func TestHighPass(t *testing.T) {
+	// Generate an audio buffer to run test on.
+	genAudio, err := generate()
+	if err != nil {
+		t.Fatal(err)
+	}
+	var buf = Buffer{Data: genAudio, Format: BufferFormat{SFormat: S16_LE, Rate: sampleRate, Channels: 1}}
+
+	// Create a highpass filter to test.
+	const fc = 4500.0
+	hp, err := NewHighPass(fc, buf.Format, filterLength)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Filter the audio.
+	filteredAudio, err := hp.Apply(buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Take the FFT of signal.
+	filteredFloats, err := bytesToFloats(filteredAudio)
+	if err != nil {
+		t.Fatal(err)
+	}
+	filteredFFT := fft.FFTReal(filteredFloats)
+
+	// Check if the highpass filter worked (any high values in filteredFFT below cutoff freq result in fail).
+	for i := 0; i < int(fc); i++ {
+		mag := math.Pow(cmplx.Abs(filteredFFT[i]), 2)
+		if mag > freqTest {
+			t.Error("Highpass Filter doesn't meet Spec", i)
+		}
+	}
+
+	// Read audio from the test location.
+	const fileName = "../../../test/test-data/av/input/hp_4500.pcm"
+	expectedAudio, err := os.ReadFile(fileName)
+	if err != nil {
+		t.Fatalf("File for comparison not read.\n\t%s", err)
+	}
+
+	// Compare against expected results.
+	compare(expectedAudio, filteredAudio, t)
+}
+
+// TestBandPass is used to test the bandpass constructor and application. Testing is done by ensuring frequency response as well as
+// comparing against an expected audio file.
+func TestBandPass(t *testing.T) {
+	// Generate an audio buffer to run test on.
+	genAudio, err := generate()
+	if err != nil {
+		t.Fatal(err)
+	}
+	var buf = Buffer{Data: genAudio, Format: BufferFormat{SFormat: S16_LE, Rate: sampleRate, Channels: 1}}
+
+	// Create a bandpass filter to test.
+	const (
+		fc_l = 4500.0
+		fc_u = 9500.0
+	)
+	hp, err := NewBandPass(fc_l, fc_u, buf.Format, filterLength)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Filter audio with filter.
+	filteredAudio, err := hp.Apply(buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Take FFT of signal.
+	filteredFloats, err := bytesToFloats(filteredAudio)
+	if err != nil {
+		t.Fatal(err)
+	}
+	filteredFFT := fft.FFTReal(filteredFloats)
+
+	// Check if the bandpass filter worked (any high values in filteredFFT above cutoff or below cutoff freq result in fail).
+	for i := 0; i < int(fc_l); i++ {
+		mag := math.Pow(cmplx.Abs(filteredFFT[i]), 2)
+		if mag > freqTest {
+			t.Error("Bandpass Filter doesn't meet Spec", i)
+		}
+	}
+
+	for i := int(fc_u); i < sampleRate/2; i++ {
+		mag := math.Pow(cmplx.Abs(filteredFFT[i]), 2)
+		if mag > freqTest {
+			t.Error("Bandpass Filter doesn't meet Spec", i)
+		}
+	}
+
+	// Read audio from test location.
+	const fileName = "../../../test/test-data/av/input/bp_4500-9500.pcm"
+	expectedAudio, err := os.ReadFile(fileName)
+	if err != nil {
+		t.Fatalf("File for comparison not read.\n\t%s", err)
+	}
+
+	// Compare against the expected audio.
+	compare(expectedAudio, filteredAudio, t)
+}
+
+// TestBandPass is used to test the bandpass constructor and application. Testing is done by ensuring frequency response as well as
+// comparing against an expected audio file.
+func TestBandStop(t *testing.T) {
+	// Generate an audio buffer to run test on.
+	genAudio, err := generate()
+	if err != nil {
+		t.Fatal(err)
+	}
+	var buf = Buffer{Data: genAudio, Format: BufferFormat{SFormat: S16_LE, Rate: sampleRate, Channels: 1}}
+
+	// Create a bandpass filter to test.
+	const (
+		fc_l = 4500.0
+		fc_u = 9500.0
+	)
+	bs, err := NewBandStop(fc_l, fc_u, buf.Format, filterLength)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Filter audio with filter.
+	filteredAudio, err := bs.Apply(buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Take FFT of signal.
+	filteredFloats, err := bytesToFloats(filteredAudio)
+	if err != nil {
+		t.Fatal(err)
+	}
+	filteredFFT := fft.FFTReal(filteredFloats)
+
+	// Check if the bandpass filter worked (any high values in filteredFFT above cutoff or below cutoff freq result in fail).
+	for i := int(fc_l); i < int(fc_u); i++ {
+		mag := math.Pow(cmplx.Abs(filteredFFT[i]), 2)
+		if mag > freqTest {
+			t.Error("BandStop Filter doesn't meet Spec", i)
+		}
+	}
+
+	// Read audio from test location.
+	const fileName = "../../../test/test-data/av/input/bs_4500-9500.pcm"
+	expectedAudio, err := os.ReadFile(fileName)
+	if err != nil {
+		t.Fatalf("File for comparison not read.\n\t%s", err)
+	}
+
+	// Compare against the expected audio.
+	compare(expectedAudio, filteredAudio, t)
+}
+
+// TestAmplifier is used to test the amplifier constructor and application. Testing is done by checking the maximum value before and
+// after application, as well as comparing against an expected audio file.
+func TestAmplifier(t *testing.T) {
+	// Load a simple sine wave with amplitude of 0.1 and load into buffer.
+	const audioFileName = "../../../test/test-data/av/input/sine.pcm"
+	lowSine, err := os.ReadFile(audioFileName)
+	if err != nil {
+		t.Errorf("File for filtering not read.\n\t%s", err)
+		t.FailNow()
+	}
+	var buf = Buffer{Data: lowSine, Format: BufferFormat{SFormat: S16_LE, Rate: sampleRate, Channels: 1}}
+
+	// Create an amplifier filter.
+	const factor = 5.0
+	amp := NewAmplifier(factor)
+
+	// Apply the amplifier to the audio.
+	filteredAudio, err := amp.Apply(buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Find the maximum sample before and after amplification.
+	dataFloats, err := bytesToFloats(buf.Data)
+	if err != nil {
+		t.Fatal(err)
+	}
+	preMax := max(dataFloats)
+	filteredFloats, err := bytesToFloats(filteredAudio)
+	if err != nil {
+		t.Fatal(err)
+	}
+	postMax := max(filteredFloats)
+
+	// Compare the values.
+	if preMax*factor > 1 && postMax > 0.99 {
+	} else if postMax/preMax > 1.01*factor || postMax/preMax < 0.99*factor {
+		t.Error("Amplifier failed to meet spec, expected:", factor, " got:", postMax/preMax)
+	}
+
+	// Load expected audio file.
+	const compFileName = "../../../test/test-data/av/input/amp_5.pcm"
+	expectedAudio, err := os.ReadFile(compFileName)
+	if err != nil {
+		t.Fatalf("File for comparison not read.\n\t%s", err)
+	}
+
+	// Compare against the expected audio file.
+	compare(filteredAudio, expectedAudio, t)
+}
+
+// generate returns a byte slice in the same format that would be read from a PCM file.
+// The function generates a sound with a range of frequencies for testing against,
+// with a length of 1 second.
+func generate() ([]byte, error) {
+	// Create an slice to generate values across.
+	t := make([]float64, sampleRate)
+	s := make([]float64, sampleRate)
+	// Define spacing of generated frequencies.
+	const (
+		deltaFreq = 1000
+		maxFreq   = 21000
+		amplitude = float64(deltaFreq) / float64((maxFreq - deltaFreq))
+	)
+	for n := 0; n < sampleRate; n++ {
+		t[n] = float64(n) / float64(sampleRate)
+		// Generate sinewaves of different frequencies.
+		s[n] = 0
+		for f := deltaFreq; f < maxFreq; f += deltaFreq {
+			s[n] += amplitude * math.Sin(float64(f)*2*math.Pi*t[n])
+		}
+	}
+	// Return the spectrum as bytes (PCM).
+	bytesOut, err := floatsToBytes(s)
+	if err != nil {
+		return nil, err
+	}
+	return bytesOut, nil
+}
+
+// compare takes in two audio files (S16_LE), compares them, and returns an error if the
+// signals are more than 10% different at any individual sample.
+func compare(a, b []byte, t *testing.T) {
+	// Convert to floats to compare.
+	aFloats, err := bytesToFloats(a)
+	if err != nil {
+		t.Fatal(err)
+	}
+	bFloats, err := bytesToFloats(b)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Compare against filtered audio.
+	for i := range aFloats {
+		diff := (bFloats[i] - aFloats[i])
+		if math.Abs(diff) > 0.1 {
+			t.Error("Filtered audio is too different to database")
+			return
+		}
+	}
+}
+
+// max takes a float slice and returns the absolute largest value in the slice.
+func max(a []float64) float64 {
+	var runMax float64 = -1
+	for i := range a {
+		if math.Abs(a[i]) > runMax {
+			runMax = math.Abs(a[i])
+		}
+	}
+	return runMax
+}

go.mod

@@ -12,10 +12,12 @@ require (
 	github.com/google/go-cmp v0.4.1
 	github.com/kidoman/embd v0.0.0-20170508013040-d3d8c0c5c68d
 	github.com/mewkiz/flac v1.0.5
+	github.com/mjibson/go-dsp v0.0.0-20180508042940-11479a337f12
 	github.com/pkg/errors v0.9.1
 	github.com/yobert/alsa v0.0.0-20180630182551-d38d89fa843e
 	gocv.io/x/gocv v0.29.0
-	gonum.org/v1/gonum v0.9.3
+	golang.org/x/tools v0.5.0 // indirect
-	gonum.org/v1/plot v0.10.0
+	gonum.org/v1/gonum v0.8.2
+	gonum.org/v1/plot v0.9.0
 	gopkg.in/natefinch/lumberjack.v2 v2.0.0
 )

go.sum

@@ -16,13 +16,11 @@ github.com/Shopify/toxiproxy v2.1.4+incompatible h1:TKdv8HiTLgE5wdJuEML90aBgNWso
 github.com/Shopify/toxiproxy v2.1.4+incompatible/go.mod h1:OXgGpZ6Cli1/URJOF1DMxUHB2q5Ap20/P/eIdh4G0pI=
 github.com/adrianmo/go-nmea v1.1.1-0.20190109062325-c448653979f7/go.mod h1:HHPxPAm2kmev+61qmkZh7xgZF/7qHtSpsWppip2Ipv8=
 github.com/aerth/playwav v0.0.0-20170324024803-17dfe21a406f/go.mod h1:aTANbm/GXj1ilCRMsIiSpX0i7LUkqjAPj6R0fpWbLNA=
+github.com/ajstarks/svgo v0.0.0-20180226025133-644b8db467af h1:wVe6/Ea46ZMeNkQjjBW6xcqyQA/j5e0D6GytH95g0gQ=
 github.com/ajstarks/svgo v0.0.0-20180226025133-644b8db467af/go.mod h1:K08gAheRH3/J6wwsYMMT4xOr94bZjxIelGM0+d/wbFw=
-github.com/ajstarks/svgo v0.0.0-20210923152817-c3b6e2f0c527 h1:NImof/JkF93OVWZY+PINgl6fPtQyF6f+hNUtZ0QZA1c=
-github.com/ajstarks/svgo v0.0.0-20210923152817-c3b6e2f0c527/go.mod h1:K08gAheRH3/J6wwsYMMT4xOr94bZjxIelGM0+d/wbFw=
 github.com/andreyvit/diff v0.0.0-20170406064948-c7f18ee00883 h1:bvNMNQO63//z+xNgfBlViaCIJKLlCJ6/fmUseuG0wVQ=
 github.com/andreyvit/diff v0.0.0-20170406064948-c7f18ee00883/go.mod h1:rCTlJbsFo29Kk6CurOXKm700vrz8f0KW0JNfpkRJY/8=
 github.com/boombuler/barcode v1.0.0/go.mod h1:paBWMcWSl3LHKBqUq+rly7CNSldXjb2rDl3JlRe0mD8=
-github.com/boombuler/barcode v1.0.1/go.mod h1:paBWMcWSl3LHKBqUq+rly7CNSldXjb2rDl3JlRe0mD8=
 github.com/cheekybits/is v0.0.0-20150225183255-68e9c0620927/go.mod h1:h/aW8ynjgkuj+NQRlZcDbAbM1ORAbXjXX77sX7T289U=
 github.com/cocoonlife/goalsa v0.0.0-20160812085113-b711ae6f3eff/go.mod h1:5aLO409bJnd+jCw0t/SB/DhHkVBhPAE31lnHJnYQxy0=
 github.com/cocoonlife/testify v0.0.0-20160218172820-792cc1faeb64/go.mod h1:LoCAz53rbPcqs8Da2BjB/yDy4gxMtiSQmqnYI/DGH+U=
@@ -46,18 +44,13 @@ github.com/go-audio/wav v0.0.0-20181013172942-de841e69b884 h1:2TaXIaVA4ff/MHHezO
 github.com/go-audio/wav v0.0.0-20181013172942-de841e69b884/go.mod h1:UiqzUyfX0zs3pJ/DPyvS5v8sN6s5bXPUDDIVA5v8dks=
 github.com/go-fonts/dejavu v0.1.0 h1:JSajPXURYqpr+Cu8U9bt8K+XcACIHWqWrvWCKyeFmVQ=
 github.com/go-fonts/dejavu v0.1.0/go.mod h1:4Wt4I4OU2Nq9asgDCteaAaWZOV24E+0/Pwo0gppep4g=
-github.com/go-fonts/latin-modern v0.2.0 h1:5/Tv1Ek/QCr20C6ZOz15vw3g7GELYL98KWr8Hgo+3vk=
 github.com/go-fonts/latin-modern v0.2.0/go.mod h1:rQVLdDMK+mK1xscDwsqM5J8U2jrRa3T0ecnM9pNujks=
+github.com/go-fonts/liberation v0.1.1 h1:wBrPaMkrXFBW3qXpXAjiKljdVUMxn9bX2ia3XjPHoik=
 github.com/go-fonts/liberation v0.1.1/go.mod h1:K6qoJYypsmfVjWg8KOVDQhLc8UDgIK2HYqyqAO9z7GY=
-github.com/go-fonts/liberation v0.2.0 h1:jAkAWJP4S+OsrPLZM4/eC9iW7CtHy+HBXrEwZXWo5VM=
-github.com/go-fonts/liberation v0.2.0/go.mod h1:K6qoJYypsmfVjWg8KOVDQhLc8UDgIK2HYqyqAO9z7GY=
 github.com/go-fonts/stix v0.1.0/go.mod h1:w/c1f0ldAUlJmLBvlbkvVXLAD+tAMqobIIQpmnUIzUY=
 github.com/go-gl/glfw v0.0.0-20190409004039-e6da0acd62b1/go.mod h1:vR7hzQXu2zJy9AVAgeJqvqgH9Q5CA+iKCZ2gyEVpxRU=
+github.com/go-latex/latex v0.0.0-20210118124228-b3d85cf34e07 h1:OTlfMvwR1rLyf9goVmXfuS5AJn80+Vmj4rTf4n46SOs=
 github.com/go-latex/latex v0.0.0-20210118124228-b3d85cf34e07/go.mod h1:CO1AlKB2CSIqUrmQPqA0gdRIlnLEY0gK5JGjh37zN5U=
-github.com/go-latex/latex v0.0.0-20210823091927-c0d11ff05a81 h1:6zl3BbBhdnMkpSj2YY30qV3gDcVBGtFgVsV3+/i+mKQ=
-github.com/go-latex/latex v0.0.0-20210823091927-c0d11ff05a81/go.mod h1:SX0U8uGpxhq9o2S/CELCSUxEWWAuoCUcVCQWv7G2OCk=
-github.com/go-pdf/fpdf v0.5.0 h1:GHpcYsiDV2hdo77VTOuTF9k1sN8F8IY7NjnCo9x+NPY=
-github.com/go-pdf/fpdf v0.5.0/go.mod h1:HzcnA+A23uwogo0tp9yU+l3V+KXhiESpt1PMayhOh5M=
 github.com/go-ping/ping v0.0.0-20201115131931-3300c582a663/go.mod h1:35JbSyV/BYqHwwRA6Zr1uVDm1637YlNOU61wI797NPI=
 github.com/golang/freetype v0.0.0-20170609003504-e2365dfdc4a0 h1:DACJavvAHhabrF08vX0COfcOBJRhZ8lUbR+ZWIs0Y5g=
 github.com/golang/freetype v0.0.0-20170609003504-e2365dfdc4a0/go.mod h1:E/TSTwGwJL78qG/PmXZO1EjYhfJinVAhrmmHX6Z8B9k=
@@ -79,17 +72,18 @@ github.com/mattetti/audio v0.0.0-20180912171649-01576cde1f21 h1:Hc1iKlyxNHp3CV59
 github.com/mattetti/audio v0.0.0-20180912171649-01576cde1f21/go.mod h1:LlQmBGkOuV/SKzEDXBPKauvN2UqCgzXO2XjecTGj40s=
 github.com/mewkiz/flac v1.0.5 h1:dHGW/2kf+/KZ2GGqSVayNEhL9pluKn/rr/h/QqD9Ogc=
 github.com/mewkiz/flac v1.0.5/go.mod h1:EHZNU32dMF6alpurYyKHDLYpW1lYpBZ5WrXi/VuNIGs=
+github.com/mjibson/go-dsp v0.0.0-20180508042940-11479a337f12 h1:dd7vnTDfjtwCETZDrRe+GPYNLA1jBtbZeyfyE8eZCyk=
+github.com/mjibson/go-dsp v0.0.0-20180508042940-11479a337f12/go.mod h1:i/KKcxEWEO8Yyl11DYafRPKOPVYTrhxiTRigjtEEXZU=
 github.com/pascaldekloe/goe v0.1.0/go.mod h1:lzWF7FIEvWOWxwDKqyGYQf6ZUaNfKdP144TG7ZOy1lc=
+github.com/phpdave11/gofpdf v1.4.2 h1:KPKiIbfwbvC/wOncwhrpRdXVj2CZTCFlw4wnoyjtHfQ=
 github.com/phpdave11/gofpdf v1.4.2/go.mod h1:zpO6xFn9yxo3YLyMvW8HcKWVdbNqgIfOOp2dXMnm1mY=
 github.com/phpdave11/gofpdi v1.0.12/go.mod h1:vBmVV0Do6hSBHC8uKUQ71JGW+ZGQq74llk/7bXwjDoI=
-github.com/phpdave11/gofpdi v1.0.13/go.mod h1:vBmVV0Do6hSBHC8uKUQ71JGW+ZGQq74llk/7bXwjDoI=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
 github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/ruudk/golang-pdf417 v0.0.0-20181029194003-1af4ab5afa58/go.mod h1:6lfFZQK844Gfx8o5WFuvpxWRwnSoipWe/p622j1v06w=
-github.com/ruudk/golang-pdf417 v0.0.0-20201230142125-a7e3863a1245/go.mod h1:pQAZKsJ8yyVxGRWYNEm9oFB8ieLgKFnamEyDmSA0BRk=
 github.com/sergi/go-diff v1.0.0 h1:Kpca3qRNrduNnOQeazBd0ysaKrUJiIuISHxogkT9RPQ=
 github.com/sergi/go-diff v1.0.0/go.mod h1:0CfEIISq7TuYL3j771MWULgwwjU+GofnZX9QAmXWZgo=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
@@ -102,6 +96,7 @@ github.com/tarm/serial v0.0.0-20180830185346-98f6abe2eb07/go.mod h1:kDXzergiv9cb
 github.com/yobert/alsa v0.0.0-20180630182551-d38d89fa843e h1:3NIzz7weXhh3NToPgbtlQtKiVgerEaG4/nY2skGoGG0=
 github.com/yobert/alsa v0.0.0-20180630182551-d38d89fa843e/go.mod h1:CaowXBWOiSGWEpBBV8LoVnQTVPV4ycyviC9IBLj8dRw=
 github.com/yryz/ds18b20 v0.0.0-20180211073435-3cf383a40624/go.mod h1:MqFju5qeLDFh+S9PqxYT7TEla8xeW7bgGr/69q3oki0=
+github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 go.uber.org/atomic v1.3.2 h1:2Oa65PReHzfn29GpvgsYwloV9AVFHPDk8tYxt2c2tr4=
 go.uber.org/atomic v1.3.2/go.mod h1:gD2HeocX3+yG+ygLZcrzQJaqmWj9AIm7n08wl/qW/PE=
 go.uber.org/multierr v1.1.0 h1:HoEmRHQPVSqub6w2z2d2EOVs2fjyFRGyofhKuyDq0QI=
@@ -115,6 +110,7 @@ golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACk
 golang.org/x/crypto v0.0.0-20190510104115-cbcb75029529/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/crypto v0.0.0-20210711020723-a769d52b0f97/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
+golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
 golang.org/x/exp v0.0.0-20180321215751-8460e604b9de/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/exp v0.0.0-20180807140117-3d87b88a115f/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/exp v0.0.0-20190125153040-c74c464bbbf2/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
@@ -129,17 +125,22 @@ golang.org/x/image v0.0.0-20200119044424-58c23975cae1/go.mod h1:FeLwcggjj3mMvU+o
 golang.org/x/image v0.0.0-20200430140353-33d19683fad8/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
 golang.org/x/image v0.0.0-20200618115811-c13761719519/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
 golang.org/x/image v0.0.0-20201208152932-35266b937fa6/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
+golang.org/x/image v0.0.0-20210216034530-4410531fe030 h1:lP9pYkih3DUSC641giIXa2XqfTIbbbRr0w2EOTA7wHA=
 golang.org/x/image v0.0.0-20210216034530-4410531fe030/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
-golang.org/x/image v0.0.0-20210607152325-775e3b0c77b9/go.mod h1:023OzeP/+EPmXeapQh35lcL3II3LrY8Ic+EFFKVhULM=
-golang.org/x/image v0.0.0-20210628002857-a66eb6448b8d h1:RNPAfi2nHY7C2srAV8A49jpsYr0ADedCk1wq6fTMTvs=
-golang.org/x/image v0.0.0-20210628002857-a66eb6448b8d/go.mod h1:023OzeP/+EPmXeapQh35lcL3II3LrY8Ic+EFFKVhULM=
 golang.org/x/mobile v0.0.0-20190719004257-d2bd2a29d028/go.mod h1:E/iHnbuqvinMTCcRqshq8CkpyQDoeVncDDYHnLhea+o=
 golang.org/x/mod v0.1.0/go.mod h1:0QHyrYULN0/3qlju5TqG8bIK38QM8yzMo5ekMj3DlcY=
+golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
+golang.org/x/mod v0.7.0 h1:LapD9S96VoQRhi/GrNTqeBJFrUjs5UHCAtTlgwA5oZA=
+golang.org/x/mod v0.7.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.0.0-20200904194848-62affa334b73/go.mod h1:/O7V0waA8r7cgGh81Ro3o1hOxt32SMVPicZroKQ2sZA=
 golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
+golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
+golang.org/x/net v0.5.0/go.mod h1:DivGGAXEgPSlEBzxGzZI+ZLohi+xUj054jfeKui00ws=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190312061237-fead79001313/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
@@ -149,34 +150,43 @@ golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20210304124612-50617c2ba197/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20210909193231-528a39cd75f3/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
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