目录

• 总览
• • SoundPlayer.java
  • MainActivicty.java

总览

Project中主要的代码在这几个文件中，控制声波发送的代码主要在MainActivity.java和SoundPlayer.java中。

SoundPlayer.java

void genTone(){ 
        // fill out the array
        for (int i = 0; i < numSamples; ++i) { 

            sample[i]=0;
              for(int j=0;j<numfreq;j++) { 
                sample[i] =sample[i]+ Math.cos(2 * Math.PI * i / (sampleRate / (freqOfTone[j])));//第i个采样点，t为i/sampleRate
            }
            sample[i]=sample[i]/numfreq;
        }

        // convert to 16 bit pcm sound array
        // assumes the sample buffer is normalised.
        int idx = 0;
        for (final double dVal : sample) { 
            // scale to maximum amplitude
            final short val = (short) ((dVal * 30000));//加振幅，加音量
            // in 16 bit wav PCM, first byte is the low order byte
            generatedSound[idx++] = (byte) (val & 0x00ff);//低8位
            generatedSound[idx++] = (byte) ((val & 0xff00) >>> 8);//高8位

        }
    }

该函数是生成声波的函数，先填入sample数组每个采样点的值。这里的声波是多个频率的cos函数相加除以频率数，论文中表示使用多个频率是为了减轻多径效应的影响。接着，该函数将声波的振幅调到最大，并且将声波信号转换成PCM编码，存入generatedSound数组中。sample[0]的低8位放在generatedSound[0]中，高8位放在generatedSound[1]中；然后sample[1]的低8位放在generatedSound[2]中，且将高8位放在generatedSound[3]中，以此类推。

public void PrepareSound() { 
        genTone();

        Log.d("llap", "" +audioTrack.write(generatedSound, 0, generatedSound.length));//write函数向audioTrack写入声波数据
        audioTrack.setLoopPoints(0, generatedSound.length / 2, -1);//循环
    }

该函数先调用genTone()函数，genTone()函数执行完后要发送的声波信号就转换为PCM编码储存在generatedSound数组中了。Log函数是把信息写到日志里，audioTrack.write函数将声波信号的PCM编码generatedSound写入audioTrack中，audioTrack.setLoopPoints函数用于设置循环数，把loopcount设置成了-1，表示无限循环。

SoundPlayer(int setsamplerate, int setnumfreq, double setfreqs[]) { 


        sampleRate=setsamplerate;
        numfreq=setnumfreq;
        for (int i=0;i<numfreq;i++)
        { 
            freqOfTone[i]=setfreqs[i];
        }
        //STREAM_MUSIC STREAM_VOICE_CALL
        audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC, sampleRate, AudioFormat.CHANNEL_OUT_MONO,
                AudioFormat.ENCODING_PCM_16BIT, generatedSound.length, AudioTrack.MODE_STATIC);//初始化

        PrepareSound();
    }

该函数是SoundPlayer类的构造函数，给freqOfTone数组赋值，new一个audioTrack，调用PrepareSound函数生成声波并将声波的PCM编码传给AudioTrack。

MainActivicty.java

//初始化wavefreqs数组和wavelength数组
        for(int i=0;i<numfreq;i++)
        { 
            wavefreqs[i]=startfreq+i*freqinter;//直线，初始化，startfreq = 15050，freqinter = 350
            wavelength[i]=soundspeed/wavefreqs[i]*1000;
        }

此段代码在用于初始化wavefreqs数组和wavelength数组。

btnPlayRecord.setOnClickListener(new OnClickListener()
        { 
            @Override
            public void onClick(View v)
            { 
                btnPlayRecord.setEnabled(false);
                btnStopRecord.setEnabled(true);

                recBufSize = AudioRecord.getMinBufferSize(sampleRateInHz,
                        channelConfig, encodingBitrate);

                mylog( "recbuffersize:" + recBufSize);

                playBufSize = AudioTrack.getMinBufferSize(sampleRateInHz,
                        channelConfig, encodingBitrate);

                audioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC,
                        sampleRateInHz, channelConfig, encodingBitrate, recBufSize);


                mylog("channels:" + audioRecord.getChannelConfiguration());

                new ThreadInstantPlay().start();
                new ThreadInstantRecord().start();
                new ThreadSocket().start();
            }
        });

该事件监听器负责配置audioRecord并且启动发送声波信号的线程。

    class ThreadInstantPlay extends Thread
    { 
        @Override
        public void run()
        { 
            SoundPlayer Player= new SoundPlayer(sampleRateInHz,numfreq,wavefreqs);
            blnPlayRecord=true;
            Player.play();
            while (blnPlayRecord==true){ }
            Player.stop();
        }
    }

该线程是发送声波信号的线程，new一个SoundPlayer并且调用play()方法发送声波。