Introduction

Briefly, the convertor works as follows :
  1. Replace the input UTF text to the corresponding phonetic symbols in our database.This is easily achieved by a careful mapping of the UTF symbols for Hindi onto the phonetic symbols in our database.Simultaneously, each symbol is tagged as a Consonant(C),Vowel(V), or Halant(H) All this is implememnted in the functions replace (for words) and replacenum (for numbers).

  2. Now we must parse the phonetic strings thus obtained to produce speakable tokens - but this is not as easy as it sounds - in fact, it's quite involved.

    The main challenge lies in a peculiarity of the Hindi language - the occasional presence of an implicit 'a' (as in the English word 'pun') in a consonant sound. This implicit vowel obviously alters the pronunciation of a word quite drastically.

    The challenge, therefore, is to come up with an algorithm that can accomodate this peculiarity and still produce the desired pronunciation, ie the desired phonetic output.

    The algorithm that we have implemented seems to work for all simple words. It may occasionally produce erroneous pronunciations for compound words, ie words made up of two or more simpler words.

The Algorithm for Parsing a Hindi Word into Speakable Tokens

The basic idea is to parse a given hindi word & produce speakable sounds, which must be of the form :

The input is a string of {C,V,Ch,""} where Ch stands for a consonant followed by a halant, and "" stands for a blank.

Let the alphabet being considered at any given time be denoted by c(n), the previous (counting from left to right) as c(n-1), etc

Parsing is done from right to left, as follows :

  1. First of all, if the word ends in a C, make it Ch. This is done in order to make the pronunciation consistent with conventional spoken hindi.
  2. Now, parse the word recursively as follows : If c(n) is : 
    (a)A "C" :
            c(n-1)         output
           ________       _________
              ""             C1
              V              CVC,if c(n-2) is a C; else CV
              C              C1C
              Ch             C1C

(b)A "Ch" :
         
             c(n-1)         output
           ________       _________
              ""             0C
              V              CVC,if c(n-2) is a C; else VC
              C              C1C
              Ch             CHCV if c(n) & c(n+1) are a CV pair  & the corresponding 'half' sound is available; else 0C

(c)A "V" :
          
             c(n-1)         output
           ________       _________
              ""             V
              V              V
              C              CV
              Ch             CV

Examples

Consider the word "Samaaroh"(Function), for example. In our phonetic symbols, this becomes "sm2r12h", and the desired phonetic output of the convertor should be "s1 m2 r12h".

Now let's see how our algorithm processes this input : We can write this "CCVCVC" in terms of consonat, vowel etc First of all, since it ends in a C, we add a halant, so we get "CCVCVCh". The length of the input is 6. Going from right to left, the algorithm works as follows -

c(6) is a Ch, and c(4) plus c(5) make a CV pair, thus we get a CVC - therefore we have "CVC" ie "r12h" in the output.

Next, c(2) and c(3) make a CV pair, and so we get "CV", or "m2", in the output.

Lastly, c(1) is a C all by itself so we output "C1", ie "s1" (that takes care of the implicit vowel :-) !!)

Thus we've got "r12h","m2","s1" and the final output is these in the reverse order, ie "s1 m2 r12h" as desired.

As another example, let's take the word "Naujawaanon"(Youngsters), which doesn't end in a "C" - in our phonetic symbols, this is "n13jv2n13", or "CVCCVCV", input of length 7. The desired output is "n13j v2 n13"

The algorithm works as follows : 

 c(6) and c(7) make a CV pair, so output is "n13"
 So do c(4) and c(5), so output is "v2"  
 Finally, c(1), c(2) and c(3) give a CVC, thus "n13j"
Thus, we get "n13j v2 n13", (after reversal) as desired. (Actually, the last part is n13n, where 13n is to give the appropriate hindi pronuciation of the vowel, just like 2n for kahaan )

CAVEAT

The algorithm can fail for certain compound words, eg consider the word "Sabhaapati"(Chairman), ie "sbh2pt3" the desired output is "s1 bh2 p1 t3".

The input is "CCVCCV", of length 6.

Now let's see how the algorithm works : 

 First c(5) and c(6) make a CV pair, so - "t3"
 Next, c(2),c(3) and c(4) make a CVC so - "bh2p" (oops!!)
 Lastly, c(1) is a solitary "C" so - "s1"
 Thus, we get "s1 bh2p t3" - not quite what we wanted.
This is an example of how our algorithm can fail for certain compund words - evidently, this will happen when the "join" is such that the end of a previous "subword" gets included in the beginning of a "subword", eg the "bh2" from "sbh2" and "p" from "pt3" in "sbh2pt3".

An obvious (brute force!!) workaround is to have a small dictionary of such "problem" words, and check whether a given word matches any of them.If so, break it up into the corresponding subwords & parse them separately - this works satisfactorily, and we've implemented this with a few words (refer functions checkspecial() and the corresponding parts of process() in hindiphoserv.c).

It must be stressed, however, that even if the algorithm makes a mistake of the above kind, the program isn't going to crash/segfault etc - one merely gets an unexpected pronunciation :-) .

Any constructive criticism/suggestion(s) are most welcome.