Get the source code using the 'Clone or download' button or download and extract this zip file.
Download BeverlyHillbillys.mid into the source folder alongside synthmidi.m and run the following Octave commands:
>> fs=44100;
>> y=synthmidi('BeverlyHillbillys.mid',[1 2 4 5 6 7]);
>> soundsc(y,fs);
Notice that track three is not synthesised as the bass is a little over powering. You can try with it included if you like.
Many thanks Ken Schutte for his readmidi.m that saved me hours of midi file parsing.