我正在使用 Ooura FFT 计算 1024 个样本窗口中加速度计数据的 FFT。该代码工作正常,但由于某种原因它会产生非常奇怪的输出,即幅度为 10^200 量级的连续频谱。
代码如下:
OouraFFT *myFFT=[[OouraFFT alloc] initForSignalsOfLength:1024 NumWindows:10]; // had to allocate it
UIAcceleration *tempAccel = nil;
double *input=(double *)malloc(1024 * sizeof(double));
double *frequency=(double *)malloc(1024*sizeof(double));
if (input)
{
//NSLog(@"%d",[array count]);
for (int u=0; u<[array count]; u++)
{
tempAccel = (UIAcceleration *)[array objectAtIndex:u];
input[u]=tempAccel.z;
//NSLog(@"%g",input[u]);
}
}
myFFT.inputData=input; // specifies input data to myFFT
[myFFT calculateWelchPeriodogramWithNewSignalSegment]; // calculates FFT
for (int i=0;i<myFFT.dataLength;i++) // loop to copy output of myFFT, length of spectrumData is half of input data, so copy twice
{
if (i<myFFT.numFrequencies)
{
frequency[i]=myFFT.spectrumData[i]; //
}
else
{
frequency[i]=myFFT.spectrumData[myFFT.dataLength-i]; // copy twice
}
}
for (int i=0;i<[array count];i++)
{
TransformedAcceleration *NewAcceleration=[[TransformedAcceleration alloc]init];
tempAccel=(UIAcceleration*)[array objectAtIndex:i];
NewAcceleration.timestamp=tempAccel.timestamp;
NewAcceleration.x=tempAccel.x;
NewAcceleration.y=tempAccel.z;
NewAcceleration.z=frequency[i];
[newcurrentarray addObject:NewAcceleration]; // this does not work
//[self replaceAcceleration:NewAcceleration];
//[NewAcceleration release];
[NewAcceleration release];
}
TransformedAcceleration *a=nil;//[[TransformedAcceleration alloc]init]; // object containing fft of x,y,z accelerations
for(int i=0; i<[newcurrentarray count]; i++)
{
a=(TransformedAcceleration *)[newcurrentarray objectAtIndex:i];
//NSLog(@"%d,%@",i,[a printAcceleration]);
fprintf(fp,[[a printAcceleration] UTF8String]); //this is going wrong somewhow
}
fclose(fp);
[array release];
[myFFT release];
//[array removeAllObjects];
[newcurrentarray release];
free(input);
free(frequency);
最佳答案
您需要调用输入和输出数组。这是我代码中的一个错误,无法修复,因为这个库已被 Apple 的新 Accelerate 框架淘汰。
关于iphone - OouraFFT 的输出有时正确,但有时完全错误。为什么?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/2463669/