# Regard ippsDemodulateFM_CToR_16s function usage

## Regard ippsDemodulateFM_CToR_16s function usage

This function suppose to converts the frequency modulated signal to the initial demodulated form, this is a new function in IPP and it is realy useful, but there is no samples about using this function and the parameters are just for the input and output but there is no parameter for the carrier frequency or for the frequency deviation, so is there any thing missing or I did not understand how to use this function.

Syntax
IppStatus ippsDemodulateFM_CToR_16s(const Ipp16s* pSrcRe, const Ipp16s* pSrcIm, Ipp16s* pDst, int len, Ipp16sc* pDlyPoint);

Parameters
pSrcRe
Pointer to the source vector with real parts of complex elements.
pSrcIm
Pointer to the source vector with imaginary parts of complex elements.
pDst
Pointer to the destination vector.
len
Number of elements in the vector.
pDlyPoint
Pointer to the value required for operation.

I need any help in using this function.

Thank you

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Hello,

see the comments from the function expert:

Description of the Demodulator module:

To demodulate the complex input signal, the demodulator performs the following steps:

1) Calculate the derivate of the phase of the input signal. That is done by a complex multiplication with the conjugate of the previous sample.

ippsConj_32fc(complexIn, conjugatedIn+1, BLOCK_LENGTH);
ippsMul_32fc(complexIn, conjugatedIn, multiplyResult, BLOCK_LENGTH);

2) Calculate the phase of the resulting complex sample

ippsPhase_32fc(multiplyResult, angleOut,BLOCK_LENGTH);

3) The output you get here ranges from pi to pi, so, as we want a value between -1 and 1, we have to multiply with 1/pi (or for fixed point: 32768/pi).

ippsMulC_32f_I(Scale, angleOut,BLOCK_LENGTH);

That`s all.

Below is the sequence of IPP calls that emulates this function behavior:

//START
ippsRealToCplx_16s();
ippsConvert_16s32f();
ippsMulC_32f_I();//scale to -1 to 1
ippsConj_32fc();
ippsMul_32fc();
ippsPhase_32fc();
ippsMulC_32f_I(); //scale with 32768/pi to limit demodulator output to fixed point +1/-1 in 0.15
//now we will need to go fixed point again
ippsConvert_32f16s_Sfs();
//END

Thanks,
Chao

what does the parameter "pDlyPoint" mean? I don't quite understand the annotation.Can somebody give me a example of the use of the function, thanks a lot.