Newbie Wavetable question

[lalo]

Hi guys!
I'm very happy to see this new part of kvr!!
I'm learnin' c++/dsp/basic math and calculus to do my own audio stuff....
I've got that wonderful book by Curtis Roads called
"Computer Music Tutorial"

In the chapter dedicated to wavetable synthesis there's a formula about table's index and increment stuff.....

the formula is

phase_index=modL (previous_phase+increment)

The explanation is : "...The modulo operation divides the sum [previous_phase+increment] by the Table lenght (L) and keeps only the remainder....."

Now, my question is...
i.e. we have a 10 index long table (0 to 9) and we have a sample increment of 1....following that formula
we have phase_index = mod 10 / (0+1) = 0
then mod 10 / (1+1)=0, then mod 10 / (2+1) = 1 , then
mod 10 / (3+1)= 2 , mod 10 / (4+1) = 0.....
so the index sequenc is 0,0,1,2,0,4,3,2,1,0
maybe i've not understand 'cause this is a funny index sequence to read a wavetable...
can anyone tell me if i did some misunderstanding?
...well i'm pretty sure
thanx in advance
lalo

[ew]

Your first would be mod10/(10+0)=0,second would be mod10/(0+1)=1,third would be mod10/(1+1)=2,etc.
Alternatively if you aren't looking at the index as a loop,you could add a constant of -1 at the end.Then,the lookup for the first would be [mod10/(0+1)]-1=0,the second would be [mod10/(1=1)]-1=1,etc.
You're only using the remainder,so it would keep incrementing by one-I don't see where you're getting your numbers
ew

[lalo]

Oh thanx!
maybe i did'nt understand the mod operation cause to me 10/(0+1)=10 and the remainder is 0
same thing for 10/(1+1)=5 and the remainder is 0....so maybe is better u explain me the modulo operation...thanx in advance
lalo

[ew]

It's because you're looking at it backwards.It's the index that's being divided by 10,and not 10 being divided by the index.Your divisor is the constant,and not the other way around.
ew

[lalo]

Thanx a lot!!
I was thinkin' about this solution...but i did'nt understand that 1/10=0 and the reminder is 1.....
i was a fool thinkin' that 1/10=0.1...hehe....now i've understand the modulo stuff...thanx a lot ew!!!!

[ew]

Right-you've got it In a modulo operation,one output will be the highest integer that's less than or equal to the divisor(the integer result of the division),and the modulo's the remainder.
ew