byte array to double array for AutoPowerSpectrum

[ngay528]

I'm trying to analyze a wav file and get the thd.

During the wav file read, I read in the data into a (void *) array.  And depending on the bit type, depends on how I call PlotWaveform.  So in my current example, i have a mono 16 bit signal.  And I call Plot Waveform like so:

PlotWaveform (panelHandle, PANEL_CHANNEL_LEFT, channel1, samplesPerChannel, type, 1.0, 0.0, 0.0, 1.0, VAL_THIN_LINE, VAL_EMPTY_SQUARE, VAL_SOLID, 1,
              			VAL_RED);

And a perfect sine wav comes out.

Now i am trying to do the THD on the signal, but am having trouble converting my byte array to a double array.  i have the following code, but all my values I get out are to teh -319th power.

channel1 is a (void *)

double *auto_power_spectrum;
double *harmonic_amplitudes;
double *harmonic_frequencies;
double *x_axis;
double *dChannel1;
double *noise;
WindowConst windowConstants;
double df;
double thd;
double thdnoise;
int number_of_harmonics = 7;
int status;
double power_peak,freq_peak;
double phase;
double *auto_power_spectrum;			double *harmonic_amplitudes;			double *harmonic_frequencies;			double *x_axis;			double *dChannel1;			double *noise;			WindowConst windowConstants;			double df;			double thd;    		double thdnoise;			int number_of_harmonics = 7;			int status;			double power_peak,freq_peak;			double phase;

dChannel1 = malloc(samplesPerChannel*sizeof(double));
for (int i = 0; i < samplesPerChannel; i++) {
	memcpy(&dChannel1[i], (char*)channel1+i*2, 2);	
}
					
				ScaledWindow(dChannel1,samplesPerChannel,0,&windowConstants);
auto_power_spectrum = malloc(samplesPerChannel/2*sizeof(double));
					
AutoPowerSpectrum (dChannel1, samplesPerChannel, 1/(double)samplingFrequency, auto_power_spectrum, &df);
//df = (double)samplingFrequency/(double)samplesPerChannel;
					
status = PowerFrequencyEstimate (auto_power_spectrum, samplesPerChannel/2, 1000, windowConstants, df, 7, &freq_peak, &power_peak);
					
x_axis = (double *)malloc((samplesPerChannel/2)*sizeof(double));

for(int i = 0; i < (samplesPerChannel/2); i++) *(x_axis + i) = i * df;
PlotXY (PANEL, PANEL_APSGRAPH, x_axis, auto_power_spectrum,samplesPerChannel/2, VAL_DOUBLE, VAL_DOUBLE, VAL_THIN_LINE,VAL_EMPTY_SQUARE, VAL_SOLID, 1, VAL_RED);
					
harmonic_amplitudes = (double *)malloc(number_of_harmonics * sizeof(double));
				    
harmonic_frequencies = (double *)malloc(number_of_harmonics * sizeof(double));
				    
status = HarmonicAnalyzer(auto_power_spectrum, samplesPerChannel/2, samplesPerChannel, number_of_harmonics, 
				                           0, samplingFrequency, freq_peak, 
				                           harmonic_amplitudes, harmonic_frequencies, &thd, &thdnoise);
				   

SetCtrlAttribute (PANEL, PANEL_APSGRAPH, ATTR_NUM_CURSORS,
				          number_of_harmonics);

for(int i = 0; i < number_of_harmonics; i++)
 {
int BOLE;
SetCursorAttribute (PANEL, PANEL_APSGRAPH, i+1, ATTR_CURSOR_POINT_STYLE,
				            VAL_SOLID_CIRCLE);
SetCursorAttribute (PANEL, PANEL_APSGRAPH, i+1, ATTR_CROSS_HAIR_STYLE,
				            VAL_VERTICAL_LINE);
 SetCursorAttribute (PANEL, PANEL_APSGRAPH, i+1, ATTR_CURSOR_COLOR,
				            VAL_BLUE);
SetActiveGraphCursor (PANEL, PANEL_APSGRAPH, i+1);
BOLE = SetBreakOnLibraryErrors (0);
SetGraphCursor (PANEL, PANEL_APSGRAPH, i+1, *(harmonic_frequencies+i),
				                    (*(harmonic_amplitudes+i) * *(harmonic_amplitudes+i)));
SetBreakOnLibraryErrors (BOLE);
}
					
				    free(harmonic_amplitudes);
				    free(harmonic_frequencies);
				    free(auto_power_spectrum);
				    free(x_axis);
					free(dChannel1);

Can someone explain to me how I should do this?  This who bit shifting and void referencing/dereferencing stuff sure hasn't stuck yet?!

Thanks in Advance

[ngay528]

Would this be correct to save the signal as a double?

for (int i = 0; i < samplesPerChannel; i++) {
	dChannel1[i] = *((char*)channel1+i*2+1) + *((char*)channel1+i*2) << 8;
						
}

[RobertoBozzolo · Accepted solution]

I suppose ConvertArrayType () function can help you in this problem.

[ngay528]

Nice catch.  I swear I looked through the toolbox, guess it just wasn't obvious.