Oscillators

Audio oscillator classes for waveform generation

The oscillators module provides efficient waveform generation classes with both standard and optimized implementations.

IOscillator

Base template class for all oscillators. Provides common phase and frequency management.

Template Parameters

T · typename

Sample type (typically double or float)

Constructor

IOscillator(double startPhase = 0., double startFreq = 1.)

startPhase · double · default: "0.0"

Initial phase value (0.0 to 1.0)

startFreq · double · default: "1.0"

Initial frequency in Hz

Methods

Process

virtual inline T Process(double freqHz) = 0

Pure virtual method to generate the next sample.

freqHz · double

Frequency in Hz for this sample

Returns: Generated sample value

SetFreqCPS

inline void SetFreqCPS(double freqHz)

Set the oscillator frequency.

freqHz · double

Frequency in cycles per second (Hz)

SetSampleRate

void SetSampleRate(double sampleRate)

Set the sample rate for processing.

sampleRate · double

Sample rate in samples per second

Reset

void Reset()

Reset the oscillator phase to the initial start phase.

SetPhase

void SetPhase(double phase)

Set the current phase directly.

phase · double

Phase value (0.0 to 1.0)

Protected Members

mPhase · double

Current phase (0.0 to 1.0)

mPhaseIncr · double

Phase increment per sample

mSampleRate · double · default: "44100.0"

Current sample rate

mStartPhase · double

Initial phase for reset

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SinOscillator

Standard sine wave oscillator using std::sin(). Suitable for general-purpose use where performance is not critical.

Template Parameters

T · typename

Sample type (typically double or float)

Constructor

SinOscillator(double startPhase = 0., double startFreq = 1.)

startPhase · double · default: "0.0"

Initial phase value (0.0 to 1.0)

startFreq · double · default: "1.0"

Initial frequency in Hz

Methods

Process (no arguments)

inline T Process()

Generate the next sample using the current frequency setting.

Returns: Sine wave sample in range [-1.0, 1.0]

Process (with frequency)

inline T Process(double freqHz) override

Generate the next sample with per-sample frequency modulation.

freqHz · double

Frequency in Hz for this sample

Returns: Sine wave sample in range [-1.0, 1.0]

Usage Example

// Create a 440Hz sine oscillator
SinOscillator<double> osc(0.0, 440.0);
osc.SetSampleRate(44100.0);

// Generate samples
for (int i = 0; i < blockSize; i++) {
  output[i] = osc.Process();
}

// Or with per-sample frequency modulation
for (int i = 0; i < blockSize; i++) {
  double freq = 440.0 + lfo.Process() * 10.0; // vibrato
  output[i] = osc.Process(freq);
}

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FastSinOscillator

High-performance sine wave oscillator using table lookup with linear interpolation. Based on Miller Puckette’s Pure Data implementation.

This oscillator uses a clever floating-point bit manipulation technique to extract table indices and fractional parts efficiently. It’s significantly faster than SinOscillator for CPU-intensive applications.

Template Parameters

T · typename

Sample type (typically double or float)

Constructor

FastSinOscillator(double startPhase = 0., double startFreq = 1.)

startPhase · double · default: "0.0"

Initial phase value (0.0 to 1.0)

startFreq · double · default: "1.0"

Initial frequency in Hz

Methods

Process (no arguments)

inline T Process()

Generate the next sample using the current frequency setting.

Returns: Sine wave sample in range [-1.0, 1.0]

Process (with frequency)

inline T Process(double freqCPS) override

Generate the next sample with per-sample frequency modulation.

freqCPS · double

Frequency in Hz for this sample

Returns: Sine wave sample in range [-1.0, 1.0]

Lookup (static)

static inline T Lookup(double phaseRadians)

Static method to look up a sine value from the table without managing state.

phaseRadians · double

Phase in radians

Returns: Sine wave value at the given phase

ProcessBlock

void ProcessBlock(T* pOutput, int nFrames)

Process an entire block of samples for better efficiency.

pOutput · T*

Output buffer to fill with generated samples

nFrames · int

Number of samples to generate

Public Members

mLastOutput · T · default: "0.0"

Last generated output value

Usage Example

// Create a fast sine oscillator
FastSinOscillator<double> osc(0.0, 440.0);
osc.SetSampleRate(44100.0);

// Process a block of samples
double output[512];
osc.ProcessBlock(output, 512);

// Static lookup for one-off calculations
double phase = 1.57079632679; // π/2
double value = FastSinOscillator<double>::Lookup(phase); // Returns ~1.0

Performance Considerations

Table Size

Uses a 512-sample lookup table with linear interpolation

Bit Manipulation

Leverages IEEE 754 double precision format for fast indexing

Block Processing

ProcessBlock() is more efficient than calling Process() in a loop

Cache Friendly

Small table size fits in CPU cache

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Implementation Details

Phase Representation

All oscillators use normalized phase values:

• Range: 0.0 to 1.0
• Wrapping: Automatic wrapping when phase exceeds 1.0
• Precision: Double precision floating point

Frequency Calculation

Phase increment is calculated as:

mPhaseIncr = (1.0 / mSampleRate) * freqHz

FastSinOscillator Algorithm

The fast oscillator uses a technique originally by Robert Höldrich:

1. Add a magic constant (UNITBIT32 = 1572864) to the phase
2. Use a union to extract integer and fractional parts
3. Use integer part as table index
4. Use fractional part for linear interpolation
5. Achieve sub-sample accuracy without expensive conversions

This technique only works with double precision floating point values in the range [-524288, +524288]. The oscillator phase is carefully managed to stay within this range.

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Code Location

Source: IPlug/Extras/Oscillator.h:1

See Also

• LFO - Low Frequency Oscillator with tempo sync
• Envelopes - Envelope generators
• Filters - Audio filtering