Trigger and waveform question

I am studying turning soundcard into oscilloscope with circular buffer, I know others have done so but wanted a go at it myslf, but need some help.

I have a 50ms window of time being diplayed from soundcard, with 2 waveforms(10ms each) with a 30ms gap between them.I have a basic trigger, but not sure what I need for problem( below):

I was wondering if its possible to have only 1 waveform be displayed(plotted) on screen, but with the same window frame of 50ms?I know I could just shorten window from to 40ms and poof its gone, but want to have a 50ms frame that ignores second waveform.Delay after first trigger or hysteresis,not sure.Confused.I'd say im intermediate level with matlab. So dont have to baby me.

[Jayaram Theegala]

If you would like to only plot the first wave (which is in the first 10 ms period), you can omit the data from 40th to 50th milliseconds. And, the above solution will work if you are sure that the second wave will only be acquired starting at 40th millisecond. In either case it should be possible for you to just filter the soundwave you want and plot it over the time period you intend.