f = 2.0f * sin(M_PI * fc / (float)(fs * F_R));
	sv->q = 2.0f * cos(pow(q, 0.1f) * M_PI * 0.5f);
	sv->qnrm = sqrt(sv->q/2.0+0.01);
	switch(t) {
	case F_LP:
		sv->op = &(sv->l);
		break;
	case F_HP:
		sv->op = &(sv->h);
		break;
	case F_BP:
		sv->op = &(sv->b);
		break;
	case F_BR:
		sv->op = &(sv->n);
		break;
	default:
		sv->op = &(sv->p);
	}
}

/* Run one sample through the SV filter. Filter is by andy@vellocet */

static inline float run_svf(sv_filter *sv, float in) {
	float out;
	int i;

	in = sv->qnrm * in ;
	for (i=0; i < F_R; i++) {
		// very slight waveshape for extra stability
		sv->b = flush_to_zero(sv->b - sv->b * sv->b * sv->b * 0.001f);

		// regular state variable code here
		// the notch and peaking outputs are optional
		sv->h = flush_to_zero(in - sv->l - sv->q * sv->b);
		sv->b = sv->b + sv->f * sv->h;
		sv->l = flush_to_zero(sv->l + sv->f * sv->b);
		sv->n = sv->l + sv->h;
		sv->p = sv->l - sv->h;

		out = *(sv->op);
		in = out;
	}

	return out;
}
		]]>

State Variable Filter

An oversampled state variable filter with a few tweaks

Quite a nice State Variable Filter, tends to be unstable with high resonance and Q values, but good when kept under control.

sample_rate = s_rate; svf = calloc(1, sizeof(sv_filter)); setup_svf(svf, 0, 0, 0, 0); free(plugin_data->svf); b * filt_res))); } ]]> Input Output Filter type (0=none, 1=LP, 2=HP, 3=BP, 4=BR, 5=AP)

Select between no filtering, low-pass, high-pass, band-pass, band-reject and all-pass.

Filter freq

Cutoff frequency, beware of high values with low sample rates.

Filter Q

The filters Q, or cutoff slope.

Filter resonance

The filter's resonance, sort of separate from Q but very related (implemented with feedback).

Do not use with the bandpass mode.