joe.cavers

I did a search for this beforehand but couldn't find anything so I apologise if I'm repeating something that's been posted here before.

I'm building an external object for Max in C for a school assignment. We were given a basic template for an object that lets audio pass through, and we're modifying it into a 4-tap delay.

I've got the signal vectors (s_vec) coming through the object, and also the vector size of the signal (s_n), both of these are picked up fine in my perform routine. For some reason I CAN NOT get the perform routine to pick up the sample rate of the incoming signal.

I've added sp[0]->s_sr to my dspAdd section, and then added it to the perform routine in the same way I have s_n being read in, but when I use post to check the value of both values, the s_n prints as whatever the buffer is set to on the dac~ object unsurprisingly and the s_sr prints as 0. If I use post just after the dspAdd section however, the sample rate reads as 44100.

I can elaborate or post screenshots if this isn't altogether clear.

externals-in-c-sample-rate-retrieval

"I've added sp[0]->s_sr to my dspAdd section, and then added it to the perform routine in the same way I have s_n being read in..."

maybe you've got this covered, but t_signal struct ref defines s_n as int and s_sr as float. did you make sure to assign it to a float variable(and you can also make it explicit('typecast' as below)) in your perform routine?

void yourobject_dsp(t_mhnmna *x, t_signal **sp, short *count) {

    dsp_add(yourobject_perform, 5, x, sp[0]->s_n, sp[0]->s_sr, sp[0]->s_vec, sp[1]->s_vec;

    t_yourobject *x = (t_yourobject *)w[1];

i could be wrong(too tired to run a full code test right now, need sleep), but try it out if you haven't already... hope it flies.

	dsp_add(yourobject_perform, 5, x, sp[0]->s_n, sp[0]->s_sr, sp[0]->s_vec, sp[1]->s_vec;

t_int *yourobject_perform(t_int *w)
{
	t_yourobject *x = (t_yourobject *)w[1];
	int n = (int)w[2];
        float f = (float)w[3];
	t_float *in = (t_float *)w[4];
        t_float *out = (t_float *)w[5];
...
...
}

________________________________
*Never fear, Noob4Life was never here!*


Yea, that's exactly what I've got. Here's an exact replica of those two parts of code in my object:

dsp_add(mspExternalTPerform, 8, x, sp[0]->s_vec, sp[1]->s_vec, sp[2]->s_vec, sp[3]->s_vec, sp[4]->s_vec, sp[0]->s_n, sp[0]->s_sr);

The outlets are because I'm creating a delay with a quadrophonic output. All those outputs work, as does the slot with s_n in it.

My perform routine (spaces are for ease of reading here):

t_mspExternalT* x = (t_mspExternalT*)(w[1]);

float* signal_out_three = (float*)(w[5]);

/* this was given to us as a long rather than an int */

That last line should assign the sample rate to a flat variable named "sample_rate" right? But when I use this:

right after it, it returns a zero. However, the same line placed after my dsp_add line prints 44100.

t_mspExternalT* x = (t_mspExternalT*)(w[1]);
float* signal_in = (float*)(w[2]);

float* signal_out_one = (float*)(w[3]);
float* signal_out_two = (float*)(w[4]);
float* signal_out_three = (float*)(w[5]);
float* signal_out_four = (float*)(w[6]);

long num_samples = (long)(w[7]);
/* this was given to us as a long rather than an int */

The quick and simple answer is that we don't support passing floating point values as arguments to dsp_add. Only pointers and integers.

Typically one accomplishes what you are looking to do by caching the sr value in your object struct. Or you could pass as a pointer to a float for that signal's sr field (you can assume this signal memory will persist).

The quick and simple answer is that we don't support passing floating point values as arguments to dsp_add. Only pointers and integers. 

That explains why I can't get it to work!

Ok, so I'm a little confused about how to do this now, could you elaborate on the mentioned methods? How do I catch the value in my object struct? This is in the

Yes. Add a floating point variable in your object struct. Assign it in your dsp method.

typedef struct _myobject
{
    t_pxobject  ob;
    ...
    float        sr;
    ...
}t_myobject;

and in your dsp method:
...
x->sr = sp[0]->s_sr;
...


Thank you so much, got it working now. Now if I can actually get the delay to work properly...

Externals in C - Sample rate retrieval