Desktop Recorder

[klaus]

EDIT : - ToRealAmplitude is not a good name because of "Real." I thought I might call it ToAmplitudes, note the plural, but is that too close to the existing ToAmplitude method name? I will also add the complementary ToPhases method.

Perhaps:
ToAmplitudePhase
ToAmplitude
ToPhase

Best regads.

[agraham]

Originally Posted by klaus

- send, in the data() array to the FFT object, only the real values- the imaginary 0 samples are generated inernally in the FFT dll

That would waste some time. After you DIM an array .NET fills it with zeros so on a new array it is only necessary to fill in the Real values.

- get back only the first half of the real and imaginary samples, only the useful ones

I've already suggested that in the post above but I need a better name or to rename some existing methods, any suggestions?

or eventually use a 'FFT algorithm specialized for real and/or symmetric data' with the same inputs and outputs.

I'll leave that to someone who is more confident with the maths than I am.

I will make some improvements.

I'll wait till you have done that

[agraham]

Originally Posted by klaus

Perhaps:
ToAmplitudePhase
ToAmplitude
ToPhase

I've already got ToAmplitude and ToPhase. How about GetAmplitute and GetPhase or shall I do a complete rename of the existing methods? What did you intend ToAmplitudePhase to do?

[redbird]

Allow me to summarize what I understood from these detailled posts, related to my example:

Filling the array only with 4096 real bytes from my sound sample will work mathematically, giving 100% correct results, but could take more time. Is that correct to assume ?

I understand the .NET mechanism that fills an array at declaration time with zeros, and see the benefits. I also understand now how the fft library is able to handle an input with only real values anyway, as it seems to generate the zero (imag) values itself internally.

BTW, I tried both methods, and besides the probable speed difference, the results looked good every time.

In my real life app, I only look for frequencies between 33 and 166 Hertz, being 1000 to 5000 RPM "headspeed" for a 2 bladed R/C helicopter. Simply 33*60/2 and 166*60/2. And until now, in this small, lower part of the spektrum, i only encountered this 1 frequency, together with 1 harmonic with exactly half the frequency, but less than half in amplitude. So my code can easily make the difference between those two, leaving no room for error.
I visualised this by means of a graph indeed, to be able to control this.
The user is of course responsible of making a recording with no other sound sources present. All the other frequencies generated by a R/C heli are much higher, being the 2-3 times faster turning tail blades, or the even higher RPMs of the electric motor, and all harmonics I found until now.

[klaus]

Hi Andrew,

I'm coming back on my suggestion 1) transfering in the Fft.Transform function only the real data.

I had a look at your library with SharpDevelop and saw that the real and imag samples could relatively easy be treated separately.
- real data in the input, half the length than before
- so, n = data.length and no more n = data.length/2
- generate an internal array for the imag data samples
- everywhere you have data(i) or data(j) is the real input data array realdata(i)
- everywhere you have data(i+1) or data(j+1) is the internal imag data array imagdata(i)
- for the return copy the first half of the imag samples into the second half of the data array.

Just to illustrate

<font size="2">data</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">j</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] = </font></font></font></font><font size="2">data</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] - </font></font></font></font><font size="2">wd_real</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font>
</font></font><font size="2">data</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">j </font><font size="2"><font color="#006400"><font size="2"><font color="#006400">+ </font></font></font></font><font size="2"><font color="#00008b"><font size="2"><font color="#00008b">1</font></font></font></font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] = </font></font></font></font><font size="2">data</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i </font><font size="2"><font color="#006400"><font size="2"><font color="#006400">+ </font></font></font></font><font size="2"><font color="#00008b"><font size="2"><font color="#00008b">1</font></font></font></font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] - </font></font></font></font><font size="2">wd_imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font>
</font></font><font size="2">data</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] += </font></font></font></font><font size="2">wd_real</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font>
</font></font><font size="2">data</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i </font><font size="2"><font color="#006400"><font size="2"><font color="#006400">+ </font></font></font></font><font size="2"><font color="#00008b"><font size="2"><font color="#00008b">1</font></font></font></font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] += </font></font></font></font><font size="2">wd_imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font></font></font>

would become

real<font size="2">data</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">j</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] = </font><font color="black">real</font></font></font></font><font size="2"><font color="black">da</font>ta</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] - </font></font></font></font><font size="2">wd_real</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font>
</font></font><font size="2">imagdata</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">j</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] = </font><font color="black">imag</font></font></font></font><font size="2"><font color="black">d</font>ata</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] - </font></font></font></font><font size="2">wd_imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font>
</font></font><font size="2">realdata</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] += </font></font></font></font><font size="2">wd_real</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font>
</font></font><font size="2">imagdata</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] += </font></font></font></font><font size="2">wd_imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font></font></font>

Could you please have a look at this.

If this is could be done, then we do no more need two methods for Amplitude and Phase.

With ToAmplitudePhase I was thinking of a single method for getting both arrays, but two seperate functions are OK for me.

Best regards.

[agraham]

It's not quite that simple as the loop arithmetic needs altering together with some other indexing stuff but I'll have a think about restructuring the library as it has grown a bit like Topsy.

[agraham]

Try this, it's probably buggy as I haven't played with it. To keep things simple and retain the full inverse transform capability I didn't generate imaginary internal values. Dimming a new array initialised to zeroes is just as cheap in Basic4pc code as in C#.

void Transform(double[] real, double[]imag)

void Inverse(double[] real, double[] imag)

double[] CopyArray(double[] array)

double[] ToAmplitude(double[] real, double[] imag, double scale)

double[] ToPhase(double[] real, double[] imag)

ToAmpAndPhase(double[] real, double[] imag, double scale) ' half and half

double[] ToReal(double[] amplitude, double[] phase, double scale)

double[] ToImaginary(double[] amplitude, double[] phase, double scale)


EDIT :- It doesn't work. I don't understand the indexing (k) in the bitreverse method so can't get it right for separate Real and Image arrays and theres a similar problem (b) in the actual transform. I'm going back to the original algorithm but will make it accept and return separate arrays.

[agraham]

I'm beginning to wish I hadn't started this separate array stuff Try this version with the same methods listed above.

[klaus]

Hi Andrew,

I just cam back home, and looked at the library.
What version is FFTV1.2 ?
The one before your edit ?

I had a look at the FFT.cs file and found that in lines 65-68

<font size="2">real</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">j</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] = </font></font></font></font><font size="2">real</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] - </font></font></font></font><font size="2">wd_real</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font>
</font></font><font size="2">imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">j</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] = </font></font></font></font><font size="2">imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] - </font></font></font></font><font size="2">wd_imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font>
</font></font><font size="2">imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] += </font></font></font></font><font size="2">wd_real</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font>
</font></font><font size="2">imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] += </font></font></font></font><font size="2">wd_imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font></font></font>

should be

<font size="2">real</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">j</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] = </font></font></font></font><font size="2">real</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] - </font></font></font></font><font size="2">wd_real</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font>
</font></font><font size="2">imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">j</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] = </font></font></font></font><font size="2">imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] - </font></font></font></font><font size="2">wd_imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font>
</font></font><font size="2"><font color="red">real</font></font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] += </font></font></font></font><font size="2">wd_real</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font>
</font></font><font size="2">imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">[</font></font></font></font><font size="2">i</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">] += </font></font></font></font><font size="2">wd_imag</font><font size="2"><font color="#006400"><font size="2"><font color="#006400">;</font></font></font></font>

This evening I won't be at home.

Best regards.

[agraham]

Originally Posted by klaus

What version is FFTV1.2 ?

V1.1 takes a single data() array
V1.2 attempted modified algorithm to take real() and imag() arrays - FAILURE for at least two reasons.
V1.3 original alogorithm wrapped to look like V1.2