Re: [Jack-Devel] Introducing delay into simple_client.c

Thanks both,

Robin: Actually, this makes perfect sense.  I occasionally forget what
pointers are actually doing :).  As for the ringbuffer, I'll check it
out.  Thanks for the tip.

Stéphane: Cool!  And Stanford produced a users manual with examples.
I'll check it out, but for the time being I'd like to see if I could
implement something like this directly with JACK.

I'll report back when I get something,

Jason

On Tue, Oct 30, 2012 at 3:27 AM, Stéphane Letz <[hidden]> wrote:
>
> Le 30 oct. 2012 à 10:17, Robin Gareus a écrit :
>
>> On 10/30/2012 07:59 AM, Jason Martyn wrote:
>>> Hi everyone,
>>>
>>> I'm brand new to JACK and its implementation, so please bear with me.
>>> I'm looking to modify the example script simple_client.c to introduce
>>> a predetermined time delay from the input to the output.  I.e.,
>>> unmodified, simple_client.c simply copies the input to the output, and
>>> instead, I would like to take the input, delay it by t seconds, and
>>> then send it to the output.
>>>
>>> To do this, I thought I would declare an array of type
>>> jack_default_audio_sample_t and then store the input into that array
>>> until the critical time where it should start playing it to the
>>> output. The new input then overwrites the old input by cycling through
>>> the array from the beginning.
>>>
>>> Here's my process callback (with comments on my reasoning):
>>>
>>> //Initialize counting integers
>>> int i = 0;
>>> int j = 0;
>>>
>>> //Initialize storage array
>>> jack_default_audio_sample_t *prev[200]; //Note: 200 is just a test number
>>>
>>> int process (jack_nframes_t nframes, void *arg)
>>> {
>>>  //For the first 200 cycles, store input into array, don't output anything
>>>   if (i<200){
>>>
>>>       prev[i] = (jack_default_audio_sample_t *) jack_port_get_buffer
>>> (input_port, nframes);
>>>       i++;
>>>   }
>>>
>>>   //For all following cycles, play the input, starting from the
>>> beginning of the array
>>>   else {
>>>
>>>   jack_default_audio_sample_t *out = (jack_default_audio_sample_t *)
>>> jack_port_get_buffer (output_port, nframes);
>>>   memcpy (out, prev[j], sizeof (jack_default_audio_sample_t) *
>>> nframes); //Note: j is the new counting variable
>>>
>>>  //Overwrite recently played input with new input:
>>>   prev[j] = (jack_default_audio_sample_t *) jack_port_get_buffer
>>> (input_port, nframes);
>>>   j++;
>>>
>>>  //Reset array counter to 0 when it reaches the end
>>>   if (j = 200){ j = 0; } //reset j
>>>   }
>>>
>>> return 0;
>>> }
>>>
>>> If this looks way off (as in I'm missing the point of how JACK, etc.
>>> works), I'd appreciate any resources that might help me get started
>>> with regards to understanding how this all works.  I have gone through
>>> the tutorials listed on the JACK site, and have a lot of troubles
>>> trying to find anything else.
>>>
>>> Regards,
>>> Jason
>>
>> Hi Jason,
>>
>> welcome aboard! The issue with above code is
>>   prev[i] = jack_port_get_buffer(..);
>>
>> The buffer returned by jack_port_get_buffer() is only valid for the
>> current process cycle. You need to memcpy() that to a temp. queue.
>>
>> While easy in principle, things can get a bit complicated because the
>> period size can change. When the delay-line buffer wraps-around and the
>> delay-line buffer-size is not an exact multiple of the period-size, you
>> will need two memcpy()s for writing and two for reading to make it seamless.
>>
>> While it's a good exercise to code that, the easiest way is to use
>> libjack's ringbuffer which does exactly that:
>> http://jackaudio.org/files/docs/html/ringbuffer_8h.html
>>
>> HTH,
>> robin
>
>
> Using Faust :
>
> process = @(1000);  (here constant delay of 1000 samples)
>
> Using the online compiler:  http://faust.grame.fr/, you can easily produce JACK based component...
>
> Stéphane
>
>

1351616560.19110_0.ltw:2,a <CAMMKq3QkBSPoX8RaM0ifgvDnKq+Hk_txmXTwpm5cbs-9etqBdQ at mail dot gmail dot com>