Question

我希望将ADPCM数据转换为XNA的.xnb文件中的PCM数据。（这么多缩写！）

我使用了几个地方作为参考，包括： http://www.wooji-juice.com/blog/iphone-openal-ima4-adpcm.html http://www.cs.columbia.edu/~hgs/audio/dvi/p34.jpg和其他几个人。

我相信我很接近，因为我听到的声音有些相似，但输出声音中存在很多静电/损坏，我似乎无法弄清楚原因。

转换归结为两个功能。

private static byte[] convert(byte[] data) 
    { 
        byte[] convertedData = new byte[(data.Length) * 4]; 

        stepSize = 7; 
        newSample = 0; 
        index = 0; 

        var writeCounter = 0; 
        for (var x = 4; x < data.Length; x++) 
        { 
            // First 4 bytes of a block contain initialization information 
            if ((x % blockSize) < 4) 
            { 
                if (x % blockSize == 0) // New block 
                { 
                    // set predictor/NewSample and index from 
                    // the preamble of the block. 
                    newSample = (short)(data[x + 1] | data[x]); 
                    index = data[x + 2]; 
                } 

                continue; 
            } 

            // Get the first 4 bits from the byte array, 
            var convertedSample = calculateNewSample((byte)(data[x] >> 4)); // convert 4 bit ADPCM sample to 16 bit PCM sample 

            // Store 16 bit PCM sample into output byte array 
            convertedData[writeCounter++] = (byte)convertedSample >> 8; 
            convertedData[writeCounter++] = (byte)convertedSample & 0x0ff;;  

            // Convert the next 4 bits of the 8 bit array. 
            convertedSample = calculateNewSample((byte)(data[x] & 0x0f)); // convert 4 bit ADPCM sample to 16 bit PCM sample. 

            // Store 16 bit PCM sample into output byte array 
            convertedData[writeCounter++] = (byte)(convertedSample >> 8); 
            convertedData[writeCounter++] = (byte)(convertedSample & 0x0ff); 
        } 

        // Conversion complete, return data 
        return convertedData; 
    } 

    private static short calculateNewSample(byte sample) 
    { 
        Debug.Assert(sample < 16, "Bad sample!"); 

        var indexTable = new int[16] { -1, -1, -1, -1, 2, 4, 6, 8, -1, -1, -1, -1, 2, 4, 6, 8 }; 

        var stepSizeTable = new int[89] { 7, 8, 9, 10, 11, 12, 13, 14, 16, 17,  
                                        19, 21, 23, 25, 28, 31, 34, 37, 41, 45,  
                                        50, 55, 60, 66, 73, 80, 88, 97, 107, 118,  
                                        130, 143, 157, 173, 190, 209, 230, 253, 279, 307, 
                                        337, 371, 408, 449, 494, 544, 598, 658, 724, 796, 
                                        876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066,  
                                        2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358, 
                                        5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,  
                                        15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767}; 

        var sign = sample & 8; 
        var delta = sample & 7; 
        var difference = stepSize >> 3; 

        // originalsample + 0.5 * stepSize / 4 + stepSize / 8 optimization. 
        //http://www.cs.columbia.edu/~hgs/audio/dvi/p34.jpg 

        if ((delta & 4) != 0) 
            difference += stepSize; 
        if ((delta & 2) != 0) 
            difference += stepSize >> 1; 
        if ((delta & 1) != 0) 
            difference += stepSize >> 2; 

        if (sign != 0) 
            newSample -= (short)difference; 
        else 
            newSample += (short)difference; 

        // Increment index 
        index += indexTable[sample]; 

        index = (int)MathHelper.Clamp(index, 0, 88); 

        newSample = (short)MathHelper.Clamp(newSample, -32768, 32767); // clamp between appropriate ranges 

        // compute new stepSize. 
        stepSize = stepSizeTable[index]; 

        return newSample; 
    }

我不相信实际的calculateNewSample（）函数是不正确的，因为我已经传递了来自http://www.cs.columbia.edu/~hgs/audio/dvi/p35.jpg的输入值，并收到了相同的输出。我已经尝试在高/低位字节之间翻转，看看我是否已经倒退也无济于事。我觉得可能有一些基本的东西，我错过了，但我很难找到它。

任何帮助都会受到重视。

在XNA中将ADPCM转换为PCM的问题

0 个答案: