Chirp

Chirp

Chirp Wave

Chirp Wave generator.

Generates a Wave that "chirps" between two frequencies.

Outputs

Wave

Chirps have an unusual envelope.

They gets softer as it approaches the half, then louder as it approaches the end.

This makes chirps a tricky sound to combine, as they slighty "pop" if directly combined.

This effect will be significantly less noticeable with rests in between each chirp.

Parameters

Frequency

The frequency

required	type	position	pipeline	wildcard	aliases
false	Object	1	false	false

Distance

The distance to the end of the chirp, in semitones

required	type	position	pipeline	wildcard	aliases
false	Double	2	false	false

Duration

The amount of time to generate.

required	type	position	pipeline	wildcard	aliases
false	TimeSpan	3	false	false

Volume

The volume

required	type	position	pipeline	wildcard	aliases
false	Double	4	false	false

Time

The start time

required	type	position	pipeline	wildcard	aliases
false	Object	5	false	false

SampleRate

The sample rate. Will default to the .SampleRate of $this wave. If there is no $this wave, will default to 44100

required	type	position	pipeline	wildcard	aliases
false	UInt32	6	false	false

channelCount

The channel count. Will default to the .ChannelCount of $this wave. If there is no $this wave, will default to 1 (mono).

required	type	position	pipeline	wildcard	aliases
false	UInt16	7	false	false

View Source

<#
.SYNOPSIS
    Chirp Wave
.DESCRIPTION
    Chirp Wave generator.
    
    Generates a Wave that "chirps" between two frequencies.
.NOTES
    Chirps have an unusual envelope.
    
    They gets softer as it approaches the half, then louder as it approaches the end.

    This makes chirps a tricky sound to combine, 
    as they slighty "pop" if directly combined.

    This effect will be significantly less noticeable with
    rests in between each chirp.
#>
[OutputType('Wave')]
param(
# The frequency
[Alias('Hz')]
$Frequency = 0,

# The distance to the end of the chirp, in semitones
[double]
$Distance = -12,

# The amount of time to generate.
[Timespan]$Duration = $(
    if ($this.BPM -is [TimeSpan]) {$this.BPM} 
    else { [TimeSpan]::FromSeconds(60/128) }
),

# The volume
[double]$Volume = $(
    if ($this.Volume) { $this.Volume }
    else { 1/([Math]::PI * 2) }
),

# The start time
$Time,

# The sample rate.
# Will default to the `.SampleRate` of `$this` wave.
# If there is no `$this` wave, will default to 44100
[uint32]$SampleRate = $(
    if ($this.SampleRate) { $this.SampleRate } else { 44100 }
),


# The channel count.
# Will default to the `.ChannelCount` of `$this` wave.
# If there is no `$this` wave, will default to 1 (mono).
[uint16]$channelCount = $(
    if ($this.ChannelCount) { $this.ChannelCount } else { 1 }
)
)

$currentWave = $this
if (-not $currentWave) { $currentWave = wave }
if (-not $PSBoundParameters['Frequency']) { $Frequency = 440 }

$fromAngles = $currentWave.MeasureAngle($Frequency, $SampleRate, $channelCount)

$toAngles = foreach ($from in $fromAngles) {
    $from * [Math]::Pow(2, (($Distance * -1.0)/12))    
}

# Calculate the number of samples
$numberOfSamples = [Math]::Round($Duration.TotalSeconds * $SampleRate * $channelCount)

$half = $numberOfSamples / 2
# Now let's make our samples
[double[]]$Samples = @(
    # Start $t at zero
    foreach ($t in 0..($numberOfSamples - 1)) {
        $ft = $t/$numberOfSamples
        #region Polysweep
        [double]$Sample = 0.0
        # Each successive angle will have a weighted volume
        # starting at full volume
        $angleWeight = 1.0
        # Take each of our angles and Add it Up
        $angles = @(
            $angleNumber = 0 
            foreach ($angle in $fromAngles) {
                $toAngle = $toAngles[$angleNumber]
                
                if ($t -lt $half) {     
                    $angle
                    # $angle + ($angle - $toAngle) * $ft/2
                } else {
                    $toAngle
                    # $toAngle - ($toAngle - $angle) * $ft/4
                }
                
                $angleNumber++
            }
        )

        foreach ($angle in $angles) {
            # Get the sine of the times and multiply by the weight.
            $Sample += [Math]::Sin($angle * $t) * $angleWeight
            # Then half the weight               
            $angleWeight/=2
        }
        #endregion Polysweep
        
        #region Envelope        
        $envelope = if ($t -lt $half) {
            1.0 - ($t / $half)
        } else {
            1.0 - ($t - $half) / ($numberOfSamples - $half)
        }        
        $sample * $Volume * $envelope
        #endregion Envelope
    }
)

# If we have not been provided a time
if (-not $time) {
    # add it to the end.
    $time = $currentWave.Duration
}

if ($Time) {
    return $currentWave.Add($samples, $time)
}
else {
    $waveFormat = $currentWave.WaveFormat
    if (-not $waveFormat) {
        $waveFormat = @{}
    }
    return wave @waveFormat -Samples $Samples
}