README.md

Sine Wave demo - 1 (Java)

This is a simple demo of sine wave generation. Sine wave generation is very similar to that used in the Lab. This demo makes use of Thread. A thread is a thread of execution in a program. The Java Virtual Machine allows an application to have multiple threads of execution running concurrently. Read more about thread here and here.

There are two buttons defined in the layout. Start button is used to start synthesizing and playing the sine wave generated and Stop button is used to stop the synthesis and playing the sine wave to the speaker.

Make the following changes to MainActivity.java and activity_main.xml.

package com.example.sinewavedemo1;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.media.AudioTrack;
import android.media.AudioFormat;
import android.media.AudioManager;

public class MainActivity extends AppCompatActivity {

    Button PlayBtn;
    Button StopBtn;
    AudioTrack Track;
    boolean isplaying = false;
    int Fs = 44100;
    int buffLength = AudioTrack.getMinBufferSize(Fs, AudioFormat.CHANNEL_OUT_MONO, AudioFormat.ENCODING_PCM_16BIT);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        PlayBtn = (Button) findViewById(R.id.PlayBtn);
        PlayBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (!isplaying) {
                    // Create a new thread to play the audio.
                    // Performing intensive operations and computations on the main UI thread,
                    // makes the app slow.
                    // That is, it is a bad idea to do intensive computations on main UI thread,
                    // so it is recommended to create a new thread to do computations in the
                    // background
                    (new Thread() {
                        @Override
                        public void run() {
                            initTrack();
                            startPlaying();
                            playback();
                        }
                    }).start();
                }

            }
        });

        StopBtn = (Button) findViewById(R.id.StopBtn);
        StopBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                stopPlaying();
            }
        });
    }

    private void initTrack() {
        // Very similar to opening a stream in PyAudio
        // In Android create a AudioTrack instance and initialize it with different
        // parameters

        Track = new AudioTrack(AudioManager.MODE_NORMAL, Fs, AudioFormat.CHANNEL_OUT_MONO,
                AudioFormat.ENCODING_PCM_16BIT, buffLength, AudioTrack.MODE_STREAM);
    }

    private void startPlaying() {
        Track.play();
        isplaying = true;
    }

    private void playback() {
        // simple sine wave generator
        short[] frame_out = new short[buffLength];
        int amplitude = (int) (32767);
        int frequency = 440;
        double twopi = 8. * Math.atan(1.);
        double phase = 0.0;
        while (isplaying) {
            for (int i = 0; i < buffLength; i++) {
                frame_out[i] = (short) (amplitude * Math.sin(phase));
                phase += twopi * frequency / Fs;
                if (phase > twopi) {
                    phase -= twopi;
                }
            }
            Track.write(frame_out, 0, buffLength);
        }
    }

    private void stopPlaying() {
        if (isplaying) {
            isplaying = false;
            // Stop playing the audio data and release the resources
            Track.stop();
            Track.release();
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:orientation="vertical"
    android:gravity="center_horizontal">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dp"
        android:text="Demo plays sine function!"
        android:textSize="30dp"
        />
    <Button
        android:id="@+id/PlayBtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="30dp"
        android:text="play"
        android:textSize="20dp"/>
    <Button
        android:id="@+id/StopBtn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Stop"
        android:textSize="20dp"/>
</LinearLayout>

Screenshots

Following are few screenshots of this demo.