From what I'm understanding so far today, if SynthMaker is limited to single precision, then SynthEdit would probably be the best place for me to start for my interest in DSP equalization. Just to make sure I'm understanding you -- you're not saying that single precision only comes into play at lower sample rates, are you? If not, then it sounds like it'll be SynthEdit and eventually, C++ for me. I have some very limited C++ experience, and I know that's where things will lead eventually. One step at a time though...
I don’t believe that is being said. Whatever direction you choose will get the job done for your demands are not very high. Your main objective is just a HPF/LPF. There are plenty of filters offered/discussed on Synthmaker’s forums once you begin to research. If you require double precision C++ or Synthedit may be a better choice than Synthmaker providing you can hear the difference using double precision versus single precision.
Only your ears can decide if it is worth the extra CPU load or not. It’s like using 96 kHz versus 44.1 kHz. You cannot convince someone there is an audible difference between 44.1 kHz & 96 kHz if the person cannot hear the difference. You will need to use your own judgement based on what your ears are telling you. The most we are giving you is options that may help you further down the line.
As a developer you will need to conduct your own testing and draw to your own conclusion. So the best method is to build a HPF/LPF in Synthmaker and let your ears decide.
While I dabble with equalisation I don’t fancy using filtering HPF/LPF unless an electronic crossover is involved since I am heavily into Sound Reinforcement. I’ve designed equalisers that offered adjustable frequencies from 0.5 Hertz to 200 kHz and, tested LPF as high as 900 kHz (Thats beyond a Moth's hearing) using Synthmaker. So don’t assume what you want is outside the realm of Synthmaker’s capability.
As I mentioned in my previous post, from an effects perspective, the limiting factor is almost always the designer not having the knowledge to make it possible. Patience is a virtue. If you are easily frustrated, you will not get far.
If you have the same passion creating your filter in Synthmaker as you were trying to get the Wave Player to emit sound in Synthmaker you will go far.