John - no, the pushbutton's UserData property isn't what you will need to start the recording.
One method is to use the audio recorder object. You would start the recording when the user presses the "record" button on your GUI, and stop the recording when the user presses the "stop" button. You create an audio recorder timer function that fires periodically (say every one second) and collects the latest set of samples, display the data in one plot/axes, do the FFT on that same set of samples and display it in the other plot/axes. The trick is to get the push button callbacks to have access to the audio recorder, and the timer function to have access to the plots.
Here is a brief outline of what you could do. Since you are using GUIDE, in its yourGuiName_OpeningFcn create the audio recorder and save it to the handles structure so that the record and stop (push) buttons have access to this object
function yourGuiName_OpeningFcn(hObject, eventdata, handles, varargin)
handles.output = hObject;
handles.Fs = 8192;
handles.recorder = audiorecorder(handles.Fs,8,1);
set(handles.recorder,'TimerPeriod',1,'TimerFcn',{@audioTimer,hObject});
guidata(hObject, handles);
All of the above is pretty straightforward. When we create the TimerFcn, we are specifying the handle to the function that will fire every 1 second (that is why we prepend the function audiotimer with the ampersand), and we are passing an additional parameter to this function, hObject which is the handle to the figure/GUI.
Now, in the start push button callback, we would do something like
function recordbutton_ClickedCallback(hObject, eventdata, handles)
record(handles.recorder);
Since we can access the audio recorder through the recorder field of handles, we do so and start the recording. We would do something similar for the stop button, replacing record with stop.
Finally, for the audio timer function that fires every one second, it could be defined as
function audioTimer(hObject,varargin)
In the above, hObject refers to the audio recorder, and varargin the variable array of input arguments/parameters. The first couple of lines for the body of this function could be
hFigure = varargin{2};
handles = guidata(hFigure);
samples = getaudiodata(hObject);
The above is just an outline of what you could do - there is a lot of code missing. For example, the getaudiodata(hObject) from above returns all the samples since the start of the recording, so you will have to keep track of the last sample that you extracted when the timer fired previously, so that you can extract the samples that followed that on the next firing of the timer. You can store this information to the handles structure by updating a field. Just remember to call guidata(hFigure,handles) to save this user-defined data.
The above will continue until you press the stop button. If you only want to record 15 seconds of data, then just do the following in the record button callback
record(handles.recorder,15);
You may want to start with this until you get things working as expected, and then remove the maximum number of seconds limit.
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