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131 lines
3.0 KiB
131 lines
3.0 KiB
// Copyright 2020 Justine Alexandra Roberts Tunney
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Additive White Gaussian Noise Generator
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//
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// This is based off the SpanDSP implementation, which is based off some
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// research paper.
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package dsp
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import (
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"math"
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)
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const (
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m1 = 259200
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ia1 = 7141
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ic1 = 54773
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rm1 = 1.0 / m1
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m2 = 134456
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ia2 = 8121
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ic2 = 28411
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rm2 = 1.0 / m2
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m3 = 243000
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ia3 = 4561
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ic3 = 51349
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dbm0MaxPower = 3.14 + 3.02
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)
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// Awgn contains the white noise generator state information.
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type AWGN struct {
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rms float64
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ix1 int64
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ix2 int64
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ix3 int64
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r [98]float64
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gset float64
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iset int
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}
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// Returns a new comfort noise generator. The volume param is in decibels and
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// -50.0 is a good value. The closer you get to 0.0, the louder the noise will
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// become.
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func NewAWGN(volume float64) (s *AWGN) {
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return NewAWGN_DBM0(7162534, volume)
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}
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func NewAWGN_DBM0(idum int64, level float64) (s *AWGN) {
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return NewAWGN_DBOV(idum, level-dbm0MaxPower)
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}
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func NewAWGN_DBOV(idum int64, level float64) (s *AWGN) {
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s = new(AWGN)
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if idum < 0.0 {
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idum = -idum
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}
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s.rms = math.Pow(10.0, level/20.0) * 32768.0
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s.ix1 = (ic1 + idum) % m1
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s.ix1 = (ia1*s.ix1 + ic1) % m1
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s.ix2 = s.ix1 % m2
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s.ix1 = (ia1*s.ix1 + ic1) % m1
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s.ix3 = s.ix1 % m3
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s.r[0] = 0.0
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for j := 1; j <= 97; j++ {
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s.ix1 = (ia1*s.ix1 + ic1) % m1
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s.ix2 = (ia2*s.ix2 + ic2) % m2
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s.r[j] = (float64(s.ix1) + float64(s.ix2)*rm2) * rm1
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}
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s.gset = 0.0
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s.iset = 0
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return
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}
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func (s *AWGN) Get() int16 {
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var fac, r, v1, v2, amp float64
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if s.iset == 0 {
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for {
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v1 = 2.0*s.ran1() - 1.0
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v2 = 2.0*s.ran1() - 1.0
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r = v1*v1 + v2*v2
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if r < 1.0 {
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break
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}
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}
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fac = math.Sqrt(-2.0 * math.Log(r) / r)
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s.gset = v1 * fac
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s.iset = 1
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amp = v2 * fac * s.rms
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} else {
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s.iset = 0
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amp = s.gset * s.rms
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}
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return fsaturate(amp)
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}
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func (s *AWGN) ran1() (res float64) {
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var j int64
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s.ix1 = (ia1*s.ix1 + ic1) % m1
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s.ix2 = (ia2*s.ix2 + ic2) % m2
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s.ix3 = (ia3*s.ix3 + ic3) % m3
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j = 1 + ((97 * s.ix3) / m3)
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if j > 97 || j < 1 {
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return -1
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}
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res = s.r[j]
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s.r[j] = (float64(s.ix1) + float64(s.ix2)*rm2) * rm1
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return
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}
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// TODO(jart): How does FISTP work in Plan9 assembly?
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func fsaturate(damp float64) int16 {
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if damp > float64(math.MaxInt16) {
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return math.MaxInt16
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}
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if damp < float64(math.MinInt16) {
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return math.MinInt16
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}
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return int16(damp)
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// return int16(lrint(damp))
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}
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