leansdr::filtergen Namespace Reference

Functions
void	dump_filter (const char *name, int ncoeffs, float *coeffs)
template<typename T >
void	normalize_power (int n, T *coeffs, float gain=1)
template<typename T >
void	normalize_dcgain (int n, T *coeffs, float gain=1)
template<typename T >
void	cancel_dcgain (int n, T *coeffs)
template<typename T >
int	lowpass (int order, float Fcut, T **coeffs, float gain=1)
template<typename T >
int	root_raised_cosine (int order, float Fs, float rolloff, T **coeffs)

Function Documentation

cancel_dcgain()

template<typename T >

void leansdr::filtergen::cancel_dcgain	(	int	n,
		T *	coeffs
	)

Definition at line 54 of file filtergen.h.

References i.

{
    float s = 0;
    for (int i = 0; i < n; ++i)
        s = s + coeffs[i];
    for (int i = 0; i < n; ++i)
        coeffs[i] -= s / n;
}

dump_filter()

void leansdr::filtergen::dump_filter	(	const char *	name,
		int	ncoeffs,
		float *	coeffs
	)

Definition at line 11 of file filtergen.cpp.

References i.

Referenced by root_raised_cosine().

{
    fprintf(stderr, "%s = [", name);
    for (int i = 0; i < ncoeffs; ++i)
        fprintf(stderr, "%s %f", (i ? "," : ""), coeffs[i]);
    fprintf(stderr, " ];\n");
}

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lowpass()

template<typename T >

int leansdr::filtergen::lowpass	(	int	order,
		float	Fcut,
		T **	coeffs,
		float	gain = 1
	)

Definition at line 67 of file filtergen.h.

References cos(), i, M_PI, normalize_dcgain(), sin(), and sinc().

{
    int ncoeffs = order + 1;
    *coeffs = new T[ncoeffs];
    for (int i = 0; i < ncoeffs; ++i)
    {
        float t = i - (ncoeffs - 1) * 0.5;
        float sinc = 2 * Fcut * (t ? sin(2 * M_PI * Fcut * t) / (2 * M_PI * Fcut * t) : 1);
#if 0 // Hamming
    float alpha = 25.0/46, beta = 21.0/46;
    float window = alpha - beta*cos(2*M_PI*i/order);
#else
        float window = 1;
#endif
        (*coeffs)[i] = sinc * window;
    }
    normalize_dcgain(ncoeffs, *coeffs, gain);
    return ncoeffs;
}

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normalize_dcgain()

template<typename T >

void leansdr::filtergen::normalize_dcgain	(	int	n,
		T *	coeffs,
		float	gain = 1
	)

Definition at line 42 of file filtergen.h.

References i.

Referenced by lowpass(), and root_raised_cosine().

{
    float s = 0;
    for (int i = 0; i < n; ++i)
        s = s + coeffs[i];
    if (s)
        gain /= s;
    for (int i = 0; i < n; ++i)
        coeffs[i] = coeffs[i] * gain;
}

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normalize_power()

template<typename T >

void leansdr::filtergen::normalize_power	(	int	n,
		T *	coeffs,
		float	gain = 1
	)

Definition at line 30 of file filtergen.h.

References leansdr::gen_sqrt(), and i.

{
    float s2 = 0;
    for (int i = 0; i < n; ++i)
        s2 = s2 + coeffs[i] * coeffs[i]; // TBD complex
    if (s2)
        gain /= gen_sqrt(s2);
    for (int i = 0; i < n; ++i)
        coeffs[i] = coeffs[i] * gain;
}

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root_raised_cosine()

template<typename T >

int leansdr::filtergen::root_raised_cosine	(	int	order,
		float	Fs,
		float	rolloff,
		T **	coeffs
	)

Definition at line 91 of file filtergen.h.

References cos(), dump_filter(), i, M_PI, normalize_dcgain(), sin(), and sqrt().

Referenced by DATVDemod::InitDATVFramework(), and DATVDemod::InitDATVS2Framework().

{
    float B = rolloff, pi = M_PI;
    int ncoeffs = (order + 1) | 1;
    *coeffs = new T[ncoeffs];
    for (int i = 0; i < ncoeffs; ++i)
    {
        int t = i - ncoeffs / 2;
        float c;
        if (t == 0)
            c = sqrt(Fs) * (1 - B + 4 * B / pi);
        else
        {
            float tT = t * Fs;
            float den = pi * tT * (1 - (4 * B * tT) * (4 * B * tT));
            if (!den)
                c = B * sqrt(Fs / 2) * ((1 + 2 / pi) * sin(pi / (4 * B)) + (1 - 2 / pi) * cos(pi / (4 * B)));
            else
                c = sqrt(Fs) * (sin(pi * tT * (1 - B)) + 4 * B * tT * cos(pi * tT * (1 + B))) / den;
        }
        (*coeffs)[i] = c;
    }
    normalize_dcgain(ncoeffs, *coeffs);
    return ncoeffs;
}

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