[Fpga-synth] phLUTe

[Eric Brombaugh]

Eric Brombaugh wrote:

>>> 2) I haven't used LaGrange interpolators before. Do you have a link or 
>>> reference to the structure you used here?
>> I found this very complete and extremely helpful:
>>
>> http://www.acoustics.hut.fi/~vpv/publications/vesan_vaitos/ch3_pt2_lagrange.pdf
>>
>> As you can tell from that sample, the tuning is precise enough for music.
> 
> Yes - those seem to work just fine. In my wireless communications work I 
> use something called a 'Farrow Interpolator' - it's got decent SNR and 
> distortion characteristics but it's fairly resource intensive (read 
> 'complicated'). I'm interested in learning simpler structures.

Hah! Reading through that paper I see in section 3.3.7 that the Farrow 
structures I've been using for lo these many years are considered a form 
of LaGrange interpolation. Learn something new every day.

I typically use a 3rd order Farrow with 8-tap FIR structures driving the 
polynomial chain (see figure 3.14). That eats up a lot of gates.

Eric