关于audiorecord 噪音有关问题

int frequency = 8000;
    int channelConfiguration = AudioFormat.CHANNEL_CONFIGURATION_MONO;
    int audioEncoding = AudioFormat.ENCODING_PCM_16BIT;
    File file = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/reverseme.pcm");
....

 OutputStream os = new FileOutputStream(file);
            BufferedOutputStream bos = new BufferedOutputStream(os);
            DataOutputStream dos = new DataOutputStream(bos);
             
            // Create a new AudioRecord object to record the audio.
            int bufferSize = AudioRecord.getMinBufferSize(frequency, channelConfiguration,  audioEncoding);
            AudioRecord audioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC, frequency, channelConfiguration, audioEncoding, bufferSize);
            
            short[] buffer = new short[bufferSize];   
            audioRecord.startRecording();
            int nCount = 1;
            
            while(nCount<21)
            {
                int bufferReadResult = audioRecord.read(buffer, 0, bufferSize);
                Log.i("550", Integer.toString(bufferReadResult));
                
                for (int i = 0; i < bufferReadResult; i++)
                {
                    dos.writeShort(buffer[i]);
                    Log.i("540", "123");
                }
                nCount++;
            }
            audioRecord.stop();
            dos.close();