我正在移植一个过滤器库,该过滤器库目前使用Apple特定的(加速)vDSP功能vDSP_deq22到Android(其中Accelerate不可用)。滤波器组是一组带通滤波器,每个滤波器滤波器返回其各自频带的RMS幅度。目前代码(ObjectiveC ++,改编自NVDSP)如下所示:
- (float) filterContiguousData: (float *)data numFrames:(UInt32)numFrames channel:(UInt32)channel {
// Init float to store RMS volume
float rmsVolume = 0.0f;
// Provide buffer for processing
float tInputBuffer[numFrames + 2];
float tOutputBuffer[numFrames + 2];
// Copy the two frames we stored into the start of the inputBuffer, filling the rest with the current buffer data
memcpy(tInputBuffer, gInputKeepBuffer[channel], 2 * sizeof(float));
memcpy(tOutputBuffer, gOutputKeepBuffer[channel], 2 * sizeof(float));
memcpy(&(tInputBuffer[2]), data, numFrames * sizeof(float));
// Do the processing
vDSP_deq22(tInputBuffer, 1, coefficients, tOutputBuffer, 1, numFrames);
vDSP_rmsqv(tOutputBuffer, 1, &rmsVolume, numFrames);
// Copy the last two data points of each array to be put at the start of the next buffer.
memcpy(gInputKeepBuffer[channel], &(tInputBuffer[numFrames]), 2 * sizeof(float));
memcpy(gOutputKeepBuffer[channel], &(tOutputBuffer[numFrames]), 2 * sizeof(float));
return rmsVolume;
}
如here所示,deq22通过递归函数对给定的输入向量实现双二阶滤波器。这是文档中函数的描述:
这是我到目前为止(它在Swift中,就像我已在Android上运行的其余代码库一样):
// N is fixed on init to be the same size as buffer.count, below
// 'input' and 'output' are initialised with (N+2) length and filled with 0s
func getFilteredRMSMagnitudeFromBuffer(var buffer: [Float]) -> Float {
let inputStride = 1 // hardcoded for now
let outputStride = 1
input[0] = input[N]
input[1] = input[N+1]
output[0] = output[N]
output[1] = output[N+1]
// copy the current buffer into input
input[2 ... N+1] = buffer[0 ..< N]
// Not sure if this is neccessary, just here to duplicate NVDSP behaviour:
output[2 ... N+1] = [Float](count: N, repeatedValue: 0)[0 ..< N]
// Again duplicating NVDSP behaviour, can probably just start at 0:
var sumOfSquares = (input[0] * input[0]) + (input[1] * input[1])
for n in (2 ... N+1) {
let sumG = (0...2).reduce(Float(0)) { total, p in
return total + input[(n - p) * inputStride] * coefficients[p]
}
let sumH = (3...4).reduce(Float(0)) { total, p in
return total + output[(n - p + 2) * outputStride] * coefficients[p]
}
let filteredFrame = sumG - sumH
output[n] = filteredFrame
sumOfSquares = filteredFrame * filteredFrame
}
let meanSquare = sumOfSquares / Float(N + 2) // we added 2 values by hand, before the loop
let rootMeanSquare = sqrt(meanSquare)
return rootMeanSquare
}
滤波器为deq22提供了不同的幅度输出,并且似乎在其中具有循环波动圆形“噪声”(具有恒定的输入音调,该频率的幅度上下波动)。
我已经检查过以确保每个实现之间的系数数组是相同的。每个滤波器实际上似乎“工作”,因为它拾取正确的频率(并且只有那个频率),它只是这个泵浦,并且RMS幅度输出比vDSP更安静,通常是数量级:
Naive | vDSP
3.24305e-06 0.000108608
1.57104e-06 5.53645e-05
1.96445e-06 4.33506e-05
2.05422e-06 2.09781e-05
1.44778e-06 1.8729e-05
4.28997e-07 2.72648e-05
任何人都可以看到我的逻辑问题吗?
编辑:这是结果的gif视频,具有恒定的440Hz音调。各种绿色条是各个滤带。第3个频段(此处显示)是调谐到440Hz的频段。
NVDSP版本只是按预期显示与输入音量成比例的恒定(非波动)幅度读数。
答案 0 :(得分:4)
好的,行sumOfSquares = filteredFrame * filteredFrame
应该是+=
,而不是作业。所以只计算了最后一帧,解释了很多;)
如果你想在Swift中进行一些双二阶过滤,请随意使用它。麻省理工学院许可证就像之前的NVDSP一样。