Voice Activity Detection in Node.js

Detecting human speech within audio can be an essential part of a speech recognition system. While humans can naturally discern speech from other sounds, machines require assistance to make this distinction. Engines designed for this purpose, known as Voice Activity Detectors (VADs), analyze audio input and determine whether it contains speech.

Picovoice's Cobra Voice Activity Detection engine makes it easy to detect voice activity in audio data. Cobra VAD is lightweight, compatible with any platform, and operates locally, ensuring privacy compliance with GDPR and HIPAA regulations.

Notably, Cobra VAD stands out as the most accurate VAD engine across all platforms, surpassing even Google's widely-used WebRTC VAD.

In just a few lines of code, you can start detecting voice activity in real time from a microphone using the Cobra Voice Activity Detection Node.js SDK. Let’s get started!

Install Packages

Create a project and install @picovoice/pvrecorder-node and @picovoice/cobra-node.

npm install @picovoice/pvrecorder-node @picovoice/cobra-node

• @picovoice/pvrecorder-node will be used to record microphone audio
• @picovoice/cobra-node will perform the voice activity detection

Sign up for Picovoice Console

Next, create a Picovoice Console account, and copy your AccessKey from the main dashboard. Creating an account is free, and no credit card is required!

Initialize Cobra

Create an instance of Cobra with your AccessKey:

const { Cobra } = require("@picovoice/cobra-node")

const cobra = new Cobra("${ACCESS_KEY}") // Replace with your Picovoice AccessKey

Capture Microphone Audio

Next, we need to pass audio to Cobra to perform voice activity detection. This audio can be from a microphone or a stream you receive from another source, as long as the audio frames are of a specific frame length (specified by cobra.frameLength) and the audio itself is recorded at the required sample rate (specified by cobra.sampleRate).

To record audio with the appropriate frame length, we can use PvRecorder - an audio recorder designed for real-time speech audio processing.

Create an instance of PvRecorder with cobra.frameLength, and call pvRecorder.start().

const { PvRecorder } = require("@picovoice/pvrecorder-node")

const pvRecorder = new PvRecorder(cobra.frameLength)
pvRecorder.start()

To stop recording audio, call pvRecorder.stop()

pvRecorder.stop()

Detect Voice Activity

Each call to pvRecorder.read() will return a single audioFrame that you can then pass to cobra for processing. Once processed, cobra will return a voice probability score, which is a floating-point value between 0 and 1.

try {
  const audioFrame = await pvRecorder.read()
  const voiceProbability = cobra.process(audioFrame)
  // take action based on the probability of voice
} catch (e) {}

Putting It All Together

A complete working example can look something like this:

// index.js
const { Cobra } = require("@picovoice/cobra-node")
const { PvRecorder } = require("@picovoice/pvrecorder-node")
const readline = require("readline")

const cobraDemo = async () => {
  let cobra;

  try {
    cobra = new Cobra("${ACCESS_KEY}") // Replace with your Picovoice AccessKey
  } catch (err) {
    console.error(err)
    process.exit()
  }

  const pvRecorder = new PvRecorder(cobra.frameLength)
  pvRecorder.start()

  console.log(`Using device: ${pvRecorder.getSelectedDevice()}`)
  console.log("Listening... Press ENTER to stop:")

  let isInterrupted = false
  readline.emitKeypressEvents(process.stdin)
  process.stdin.setRawMode(true)
  process.stdin.on("keypress", (key, str) => {
    if (str.sequence === "\r" || str.sequence === "\n") {
      process.stdout.write(`\nStopped\n`);
      isInterrupted = true
    }
  })

  while (!isInterrupted) {
    try {
      const audioFrame = await pvRecorder.read()
      const voiceProbability = cobra.process(audioFrame)
      process.stdout.write(voiceProbability);
    } catch (err) {
      console.error(err)
      isInterrupted = true
    }
  }

  pvRecorder?.stop()
  pvRecorder?.release()
  cobra?.release()
  process.stdout.write("\n");
  process.exit()
}

cobraDemo()

For a complete working project, take a look at the Cobra Voice Activity Detection Node.js Demo. You can also view the Cobra Voice Activity Detection Node.js API docs for details on the package.