[sdiy] Question about "Musical Applications of Microprocessors" book

[Dave Manley]

Sam Ecoff wrote:
> Hi Gang,
>
> So, at the kind advice of the list, I'm wading through "Musical 
> Applications of Microprocessors". Very enlightening, and very 
> enjoyable! I have a question, though. I was always taught that square 
> waves were composed of only the odd harmonics. I believed that meant 
> you *wouldn't* have a harmonic an octave higher than the fundamental, 
> but on pages 23-25, it shows the process of creating a square wave by 
> adding sine waves, one of which has a frequency which is double that 
> of the fundamental. I have also noticed that while some books count 
> the fundamental as the first harmonic, others treat an octave higher 
> as the first harmonic. Regardless of which system, the info in the 
> microprocessors book doesn't seem to work as they also show that you'd 
> have to combine a sine wave whose frequency is three times the 
> fundamental to get a square wave. What am I missing here?
Hi Sam,

It is because the wave being synthesized is not a square wave - the duty 
cycle is not 50%.

There are some useful examples, including pulse vs. square here: 
http://www.dspguide.com/ch13/4.htm

-Dave