增加录制音频的音量输出 [英] Increase volume output of recorded audio

问题描述

我正在尝试在 Android 中制作通话录音应用.我正在使用扬声器记录上行和下行音频.我面临的唯一问题是音量太低.我已将使用 AudioManager 的设备音量增加到最大，但无法超过.

I am trying to make a call recording app in Android. I am using loudspeaker to record both uplink and downlink audio. The only problem I am facing is the volume is too low. I've increased the volume of device using AudioManager to max and it can't go beyond that.

我第一次使用 MediaRecorder，但由于它的功能有限并且提供压缩音频，我尝试使用 AudioRecorder.我仍然没有想出如何增加音频.我也在 Github 上查看过项目，但没有用.过去两周我一直在 stackoverflow 上搜索，但根本找不到任何东西.

I've first used MediaRecorder, but since it had limited functions and provides compressed audio, I've tried with AudioRecorder. Still I havn't figured out how to increase the audio. I've checked on projects on Github too, but it's of no use. I've searched on stackoverflow for last two weeks, but couldn't find anything at all.

我很确定这是可能的，因为许多其他应用程序都在这样做.例如，自动呼叫记录器就是这样做的.

I am quite sure that it's possible, since many other apps are doing it. For instance Automatic Call recorder does that.

我知道我必须对音频缓冲区做一些事情，但我不太确定需要做些什么.你能指导我吗.

I understand that I have to do something with the audio buffer, but I am not quite sure what needs to be done on that. Can you guide me on that.

更新:-
很抱歉我忘了提及我已经在使用 Gain.我的代码几乎类似于 RehearsalAssistant(实际上我是从那里推导出来的).增益不会超过 10dB，并且不会过多地增加音频音量.我想要的是我应该能够在不将耳朵放在扬声器上的情况下收听音频，这是我的代码所缺乏的.

Update:-
I am sorry that I forgot to mention that I am already using Gain. My code is almost similar to RehearsalAssistant (in fact I derived it from there). The gain doesn't work for more than 10dB and that doesn't increase the audio volume too much. What I wanted is I should be able to listen to the audio without putting my ear on the speaker which is what lacking in my code.

我在 SoundDesign SE 上问过一个关于音量/响度功能的类似问题 此处.它提到增益和响度是相关的，但它没有设置实际的响度级别.我不确定事情是如何运作的，但我决心获得大音量输出.

I've asked a similar question on functioning of the volume/loudness at SoundDesign SE here. It mentions that the Gain and loudness is related but it doesn't set the actual loudness level. I am not sure how things work, but I am determined to get the loud volume output.

推荐答案

你显然有 AudioRecord 东西在运行，所以我跳过了 sampleRate 和 的决定输入源.主要的一点是，您需要在录音循环中适当地处理记录数据的每个样本以增加音量.像这样:

You obviously have the AudioRecord stuff running, so I skip the decision for sampleRate and inputSource. The main point is that you need to appropriately manipulate each sample of your recorded data in your recording loop to increase the volume. Like so:

    int minRecBufBytes = AudioRecord.getMinBufferSize( sampleRate, AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT );
    // ...
    audioRecord = new AudioRecord( inputSource, sampleRate, AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT, minRecBufBytes );

    // Setup the recording buffer, size, and pointer (in this case quadruple buffering)
    int recBufferByteSize = minRecBufBytes*2;
    byte[] recBuffer = new byte[recBufferByteSize];
    int frameByteSize = minRecBufBytes/2;
    int sampleBytes = frameByteSize;
    int recBufferBytePtr = 0;

    audioRecord.startRecording();

    // Do the following in the loop you prefer, e.g.
    while ( continueRecording ) {
        int reallySampledBytes = audioRecord.read( recBuffer, recBufferBytePtr, sampleBytes );

        int i = 0;
        while ( i < reallySampledBytes ) {
            float sample = (float)( recBuffer[recBufferBytePtr+i  ] & 0xFF
                                  | recBuffer[recBufferBytePtr+i+1] << 8 );

            // THIS is the point were the work is done:
            // Increase level by about 6dB:
            sample *= 2;
            // Or increase level by 20dB:
            // sample *= 10;
            // Or if you prefer any dB value, then calculate the gain factor outside the loop
            // float gainFactor = (float)Math.pow( 10., dB / 20. );    // dB to gain factor
            // sample *= gainFactor;

            // Avoid 16-bit-integer overflow when writing back the manipulated data:
            if ( sample >= 32767f ) {
                recBuffer[recBufferBytePtr+i  ] = (byte)0xFF;
                recBuffer[recBufferBytePtr+i+1] =       0x7F;
            } else if ( sample <= -32768f ) {
                recBuffer[recBufferBytePtr+i  ] =       0x00;
                recBuffer[recBufferBytePtr+i+1] = (byte)0x80;
            } else {
                int s = (int)( 0.5f + sample );  // Here, dithering would be more appropriate
                recBuffer[recBufferBytePtr+i  ] = (byte)(s & 0xFF);
                recBuffer[recBufferBytePtr+i+1] = (byte)(s >> 8 & 0xFF);
            }
            i += 2;
        }

        // Do other stuff like saving the part of buffer to a file
        // if ( reallySampledBytes > 0 ) { ... save recBuffer+recBufferBytePtr, length: reallySampledBytes

        // Then move the recording pointer to the next position in the recording buffer
        recBufferBytePtr += reallySampledBytes;

        // Wrap around at the end of the recording buffer, e.g. like so:
        if ( recBufferBytePtr >= recBufferByteSize ) {
            recBufferBytePtr = 0;
            sampleBytes = frameByteSize;
        } else {
            sampleBytes = recBufferByteSize - recBufferBytePtr;
            if ( sampleBytes > frameByteSize )
                sampleBytes = frameByteSize;
        }
    }

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