## General Guidelines for Programming DECtalk Applications

In doing real-time programming of applications of DECtalk there are some important concepts worth keeping in mind to maximise the performance of the overall system.

Clause Based Synthesis

First DECtalk processes all text on a clause basis because intonation is done on a clause basis. A clause is defined as a period, question mark, exclamation point, or question mark followed by white-space. If you send DECtalk five words with no terminator it can do little with it except wait for the rest of the clause. A "[:sync]" command will act the same as an period- white space. If the time-out command, [:Timeout d], is set DECtalk will force speak any text that has been sent to it without punctuation if no more characters have been received in the amount of time specified in the time-out command.

Error Speak

The default setting for DECtalk is with error speak on. This reports any errors that DECtalk can detect. There is one case however when an error is normal and that is during the flush command. If a flush is issued while DECtalk is in the middle of processing a command it will report a command error because the command never finished parsing. Applications should always set "[:error ignore]" on the release version.

Eliminating do-while Loops

In the demo program most of the TSR calls are put in a do-while loop because there is nothing else to be done at the time. In an real application there is often other things that can be done so you should return from a TSR_BUSY or TSR_RETRY command and do other things and try the command again later. On very high performance processors continually calling the TSR in a do while loop can actually slow things down as the processor can ask DECtalk "are you ready yet?" so often that DECtalk spends too much time saying "no" that it can get it's work done quickly.

Flow Control

Flow management is also useful. It is not normally useful to send DECtalk large blocks of text at once, because typically you end up speaking for a while and then the text gets flushed while you go do something else. If the DECtalk is kept busy inputting a large block of text it has less time to devote to processing the text. There is typically no value in having DECtalk loaded with ten minutes worth of text. The key here is to keep a sentence or two ahead of where you are and send a new sentence every time you finish one.

Indexing for Speech Status

It is easy to tell where you are with the index commands. By imbedding an index in the text you the DECtalk will tell you exactly when that text has been spoken. The indexes attach themselves to the NEXT speech sound, they bind forward. Therefore if you send "Hello. [:i m 5] " nothing will be returned until the next clause because there is nothing for it to bind to. A "Hello[:i m 5]. " will work or "Hello. [:i m 3] [:sync]" but in the second case the sync forces some extra silence through the DECtalk for the index to bind to.

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