Picovoice.Orca 1.1.1

Orca Binding for .NET

Orca Streaming Text-to-Speech Engine

Orca is an on-device streaming text-to-speech engine that is designed for use with LLMs, enabling zero-latency voice assistants. Orca is:

• Private; All speech synthesis runs locally.
• Cross-Platform:
  • Linux (x86_64), macOS (x86_64, arm64), Windows (x86_64, arm64)
  • Android and iOS
  • Raspberry Pi (3, 4, 5)
  • Chrome, Safari, Firefox, and Edge

Requirements

• .NET 8.0

Compatibility

Platform compatible with .NET Framework 4.6.1+:

• Windows (x86_64)

Platforms compatible with .NET Core 2.0+:

• macOS (x86_64)
• Windows (x86_64)

Platform compatible with .NET 6.0+:

• Raspberry Pi:
  • 3 (32 and 64 bit)
  • 4 (32 and 64 bit)
  • 5 (32 and 64 bit)
• Linux (x86_64)
• macOS (arm64)
• Windows (arm64)

Installation

You can install the latest version of Orca by getting the latest Orca Nuget package in Visual Studio or using the .NET CLI.

dotnet add package Picovoice.Orca

AccessKey

Orca requires a valid Picovoice AccessKey at initialization. AccessKey acts as your credentials when using Orca SDKs. You can get your AccessKey for free. Make sure to keep your AccessKey secret. Signup or Login to Picovoice Console to get your AccessKey.

Usage

Orca supports two modes of operation: streaming and single synthesis. In the streaming synthesis mode, Orca processes an incoming text stream in real-time and generates audio in parallel. In the single synthesis mode, a complete text is synthesized in a single call to the Orca engine.

Create an instance of the Orca engine:

using Pv;

const string accessKey = "${ACCESS_KEY}"; // Obtained from the Picovoice Console (https://console.picovoice.ai/)

Orca orca = Orca.Create(accessKey);

Replace the ${ACCESS_KEY} with your AccessKey obtained from Picovoice Console.

To synthesize a text stream, create an Orca.OrcaStream object and add text to it one-by-one:

Orca.OrcaStream stream = orca.StreamOpen();

foreach (string textChunk in TextGenerator())
{
    short[] streamPcm = orcaStream.Synthesize(textChunk);
    if (streamPcm != null)
    {
        // handle pcm chunk
    }
}

short[] flushPcm = orcaStream.Flush();
if (flushPcm != null)
{
    // handle final pcm chunk
}

The TextGenerator() function can be any stream generating text, for example an LLM response. Orca produces audio chunks in parallel to the incoming text stream, and returns the raw PCM whenever enough context has been added via orcaStream.Synthesize(). To ensure smooth transitions between chunks, the orcaStream.Synthesize() function returns an audio chunk that only includes the audio for a portion of the text that has been added. To generate the audio for the remaining text, orcaStream.Flush() needs to be invoked.

OrcaStream implements IDisposable, so you either call .Dispose() to close it or wrap it in a using statement:

using(Orca.OrcaStream stream = orca.StreamOpen())
{
    // .. OrcaStream usage here
}

If the complete text is known before synthesis, single synthesis mode can be used to generate speech in a single call to Orca:

// Return raw audio data (PCM) and alignments
OrcaAudio res = orca.Synthesize("${TEXT}");

// Save the generated audio to a WAV file directly and just return alignments
OrcaWord[] alignments = orca.SynthesizeToFile("${TEXT}", "${OUTPUT_PATH}");

Replace ${TEXT} with the text to be synthesized and ${OUTPUT_PATH} with the path to save the generated audio as a single-channel 16-bit PCM WAV file. In single synthesis mode, Orca returns metadata of the synthesized audio in the form of a list of OrcaWord objects. You can print the metadata with:

foreach (OrcaWord w in alignments)
{
    Console.WriteLine($"word=\"{w.Word}\", start_sec={w.StartSec}, end_sec={w.EndSec}");
    foreach (OrcaPhoneme p in token.Phonemes)
    {
        Console.WriteLine($"\tphoneme=\"{p.Phoneme}\", start_sec={p.StartSec}, end_sec={p.EndSec}");
    }
}

Orca will have its resources freed by the garbage collector, but to have resources freed immediately after use, wrap it in a using statement:

using(Orca orca = Orca.Create(accessKey))
{
    // .. Orca usage here
}

Text input

Orca supports a wide range of English characters, including letters, numbers, symbols, and punctuation marks. You can get a list of all supported characters with the .valid_characters property. Pronunciations of characters or words not supported by this list can be achieved with custom pronunciations.

Custom pronunciations

Orca allows to embed custom pronunciations in the text via the syntax: {word|pronunciation}.
The pronunciation is expressed in ARPAbet phonemes, for example:

• "This is a {custom|K AH S T AH M} pronunciation"
• "{read|R IY D} this as {read|R EH D}, please."
• "I {live|L IH V} in {Sevilla|S EH V IY Y AH}. We have great {live|L AY V} sports!"

Language and Voice

Orca Streaming Text-to-Speech can synthesize speech in different languages and with a variety of voices, each of which is characterized by a model file (.pv) located in lib/common. The language and gender of the speaker is indicated in the file name.

To create an instance of the engine with a specific voice, use:

Orca orca = Orca.Create(accessKey, "${MODEL_PATH}");

and replace ${MODEL_PATH} with the path to the model file with the desired voice.

Speech control

Orca allows for keyword arguments to control the synthesized speech. They can be provided to the StreamOpen method or the single synthesis methods Synthesize and SynthesizeToFile:

• speechRate: Controls the speed of the generated speech. Valid values are within [0.7, 1.3]. A higher (lower) value produces speech that is faster (slower). The default is 1.0.
• randomState: Sets the random state for sampling during synthesis. This can be used to ensure that the synthesized speech is deterministic across different runs. Valid values are all non-negative integers. If not provided, a random seed will be chosen and the synthesis process will be non-deterministic.

Orca properties

To obtain the set of valid characters, call orca.ValidCharacters.
To retrieve the maximum number of characters allowed, call orca.MaxCharacterLimit.
The sample rate of Orca is orca.SampleRate.

Alignment Metadata

Along with the raw PCM or saved audio file, Orca returns metadata for the synthesized audio in single synthesis mode. The OrcaWord object has the following properties:

• Word: String representation of the word.
• Start Time: Indicates when the word started in the synthesized audio. Value is in seconds.
• End Time: Indicates when the word ended in the synthesized audio. Value is in seconds.
• Phonemes: A list of OrcaPhoneme objects.

The OrcaPhoneme object has the following properties:

• Phoneme: String representation of the phoneme.
• Start Time: Indicates when the phoneme started in the synthesized audio. Value is in seconds.
• End Time: Indicates when the phoneme ended in the synthesized audio. Value is in seconds.

Demos

The Orca dotnet demo project is a .NET command line application that allows for synthesizing audio using Orca.