ribbon62

I have created a Max external called "Surround_process" in Visual Studio that has 2 inputs (numins) and 5 outputs (numouts). The 2 incoming audio signals must be processed and output a surround signal with 5 channels in Real time. To achieve this, each audio signal coming from the inlet will be copied to each output to have 5 output signals, and each of this signals will be multiplied with a gain factor.

The gain value is obtained using another method called set and stored in a matrix of values. This gain value comes from a slider that is connected to the input of "Surround_process" in the maxpat.

The problem is that when the slider is being moved, audible clicks appears on the output audio signal. However, when the slider is in a fixed position, the output can be heard properly, so I assume the problem ocurrs when the algorithm is interpolating each sample.

Could anyone please help me to improve the signal processing algorithm for this example?

void Surround_process::perform(double **ins, long numins, double **outs, long numouts, long sampleframes)

    for (outlet_nr = 0; outlet_nr < numouts; outlet_nr++) { //Create 5 audio signals for the outlets

        out    = outs[outlet_nr];

        for (i=0; i < sampleframes; i++) {

        for (inlet_nr = 0; inlet_nr < numins; inlet_nr++) {

            in        = ins[inlet_nr];

            gain    = m_gain[inlet_nr][outlet_nr];     // A matrix called m_gain contains the values of the gains (2 numins and 5 numouts)

            for (i=0; i < sampleframes; i++) {

                out[i] += in[i]* gain;

Hello!!
I have created a Max external called "Surround_process" in Visual Studio that has 2 inputs (numins) and 5 outputs (numouts). The 2 incoming audio signals must be processed and output a surround signal with 5 channels in Real time. To achieve this, each audio signal coming from the inlet will be copied to each output to have 5 output signals, and each of this signals will be multiplied with a gain factor.
The gain value is obtained using another method called set and stored in a matrix of values. This gain value comes from a slider that is connected to the input of "Surround_process" in the maxpat.
The problem is that when the slider is being moved, audible clicks appears on the output audio signal. However, when the slider is in a fixed position, the output can be heard properly, so I assume the problem ocurrs when the algorithm is interpolating each sample.
Could anyone please help me to improve the signal processing algorithm for this example?
void Surround_process::perform(double **ins, long numins, double **outs, long numouts, long sampleframes)
{
	double*		out;
	long		i;
	long		outlet_nr;
	long		inlet_nr ;
	double*		in;
	double		gain;

	for (outlet_nr = 0; outlet_nr < numouts; outlet_nr++) { //Create 5 audio signals for the outlets
		out	= outs[outlet_nr];

		for (i=0; i < sampleframes; i++) {
			out[i] = 0;
		}

		for (inlet_nr = 0; inlet_nr < numins; inlet_nr++) {
			in		= ins[inlet_nr];
			gain	= m_gain[inlet_nr][outlet_nr]; 	// A matrix called m_gain contains the values of the gains (2 numins and 5 numouts)
			for (i=0; i < sampleframes; i++) {

perform-method-introduces-audible-clicks-in-audio-output

actually, there is no interpolation in your example - hence the clicks.

the easiest way to solve the problem is, in my opinion, getting the gains from signal rather than message inlets. In this way, the interpolation could be done e.g. by line~ objects connected to your object's inlets.

or, of course, you can interpolate within your object: more efficient, but a bit trickier and probably less flexible.

by the way, your code has another potential problem: in general, and unless you set the Z_NO_INPLACE (or something like that) flag, you are supposed to write your n-th samples for each outlet only _after you have read all the n-th samples from each inlet, because input and output vectors in most cases use the same memory space.

in your case, you should not zero the output vector before processing the input, and the iteration upon the samples should be the outermost loop.

by the way, your code has another potential problem: in general, and unless you set the Z_NO_INPLACE (or something like that) flag, you are supposed to write your n-th samples for each outlet only _after you have read all the n-th samples from each inlet, because input and output vectors in most cases use the same memory space. 

... by the way, this thread should be moved to the Dev forum

Perform method introduces audible clicks in audio output