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Speech recognition software is only of value if it makes you more productive and your job more easy.

A good computer is one of the key parts of getting the best out of your speech recognition software.

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Accuracy and Optimizing Speech Recognition Performance

Choosing the best hardware to give you the best accuracy and performance

These days you no longer need a supercomputer for speech recognition to work well.  But you might get some appreciable benefits by upgrading your current computer.

This is part of a series on speech recognition software.  See related articles listed on the right.



How much accuracy is necessary to make speech recognition a practical consideration for you?

How fast do you need to be able to speak at so as to make speech recognition truly productive for you?

And, a related question, is your present computer system powerful enough to give you good first speech recognition? If it is not, what sort of computer system should you now upgrade to?

Please read on for the answers to these questions.

The Vital Importance of Small Improvements In Accuracy

It is easy to look at two different speech recognition systems, one offering perhaps a 97% accuracy rate and the other offering perhaps a 98% accuracy rate, and to think that the difference of 'only' 1%, especially when both systems are scoring so high, is not worth paying much extra money for.

Unfortunately, if you think this, you are looking at the process from the wrong perspective. The key concept to keep in mind is not how much the system gets correct, but how much the system gets wrong.

And so, when expressed in terms of errors, one system offers 3% errors and the other system offers 2% errors. Maybe these two numbers also seem very similar. But think about it this way : the system with 3% errors is making mistakes 50% more often than the system with 2% errors. Instead of having maybe six errors to correct in a given piece of dictation, you will have nine.  All of a sudden, a small seeming difference starts to be more realistically appreciated as very big and significant.

Keep in mind that the major hassle factor in speech recognition software is the correction process. And so you would be very well advised to chase down the most accurate system possible - that seemingly insignificant difference of only 1% actually represents a 50% increase in errors and correcting.  and that is definitely worth going to a reasonable amount of time, trouble, and investment to optimize.

How Much Accuracy Is Enough

Of course, the more accurate the results you get from your speech recognition, the very much better it will be.

There is no exact magic number, below which speech recognition is inadequate, and above which it is productive.  Assessing these values depends in part on how fast you can type, and what your other alternatives would be.

But, to provide some general guidance, it would be fair to say that if you are getting less than 95% accuracy, you will be disappointed; and if you are getting more than 98%, you will be pleased. If you reach 99%, you may even be delighted.  As you will recall from the preceding section, a move from 98% to 99% it is a profound difference - it represents a massive halving of the number of errors to be corrected.

Getting it Right First Time

If you are going to implement a speech recognition system, you should try and get your system optimized right from the very beginning.

That way you save yourself the time and inconvenience of needing to retrain your system if you make changes to it.  It also means that you'll be getting a more positive experience right from day one, and so you will be more likely to benefit from and continue to use speech recognition software.

(I write this very much in a 'Do as I say, not as I do' manner; I am on my second computer and fourth microphone in not quite three weeks of successive - and increasingly frustrating - tweaks to my set up in the ongoing quest for better performance.)

So, be sensitive to the vital importance of optimizing accuracy as far as is practicable and be open to the probable need to invest money in better equipment upfront; this will save you lots of time and frustration.

The key two things to get right are the power of your computer and the quality of your microphone.

How Much Computer Power Do You Need

How high is up?  The short answer to this question is that a more powerful computer is invariably better than a less powerful computer.

A more powerful computer gives you two important benefits when using speech recognition software.  The first benefit is that it works more quickly, and you can speak at a more natural speed and the computer will more readily keep up with you.

The second benefit is that a more powerful computer can "think harder" about what you are saying.  Instead of considering (shall we say) 10 different alternatives for what it thinks you said; it can consider 20 different alternatives in the same amount of time and increase the likelihood of determining the correct words for what it heard.

Is your present computer powerful enough

This is again a subjective question with a similarly subjective answer.  The actual speed at which a computer works depends upon several different parts of the computer, and also depends on the type of work it is doing.

In the case of speech recognition, the most important parts of the computer are the processor and its speed, the amount of cache on the processor itself, and lastly the amount of and speed of memory (not disk but memory).  Speech processing software typically resides completely in memory, and does most of its processing using the processor's onboard cache.

Apart from its initial load, the software should never need to go back out to the desk to get extra information because that would be way too slow.  It also is not a graphically intense task, so is not materially dependent on the speed of your graphics card.

Test and measure your computer

Here is a way to objectively measure your computer's real world processing power - use this free suite of three tests.

This testing suite will give you results for three different tests, and then an aggregate result averaging all three individual results.  You should look both at the scores and also the percentage CPU utilization in the three tests.  You want the scores to be high and the CPU utilization to be low.  Low scores mean an underpowered computer, and high CPU utilization suggests that the CPU is the weak link in the chain.

The least relevant of the three tests is the last one, but they are all reasonably sensible tests that relate reasonably directly to the performance you can expect with speech recognition software.

I have tested two of my main computers. The slower scored 532, the faster scored 905.

But, despite one machine scoring almost twice the other, there was not really a profound difference between the two machines in terms of performance.  The slower machine work adequately, the faster machine works better.  I was surprised at the difference in score, and immediately discontinued using the slower machine, hence the slightly imprecise nature of my evaluation.

There was one particularly surprising part of the score. The slower machine (almost 4 years old) was powered by a dual core Pentium processor, operating at 3.4 GHz. The faster machine (not yet six months old) was powered by a dual core T9600 processor, operating at 2.8 GHz. Although slower in gigahertz terms, everything else about the computer is clearly very much faster. Moral of the story?  You cannot judge a computer merely by the speed of its processor.

These days, modern processors do more things per cycle.  It is probably valid to compare one processor with another of the same generation and design, and to conclude that the one with the higher rated speed will be faster, but it is not so valid to compare processors of two different generations and to try and directly compare their productivity as if linked to their rated speeds.

I also tested an Intel Celeron 743 single core CPU powered Netbook, operating at 1.3GHz.  It scored a mere 253.

What these scores suggest, overall, is that if your computer scores less than 500, it is probably appreciably underpowered, and you should consider upgrading. If it scores over 1000, it is a good midrange computer judged by current standards of CPU power (i.e. as of May 2010).

Choosing a New Faster Computer

How to know if a new computer will be sufficiently more powerful than your old computer?  Should you spend $500, $1000, $1500, or some other sum on getting a new computer?

One possible way to get a feel for the real world improvement offered by a new computer would be to run the same test on the computer you are considering buying. This of course assumes that you have access to a computer in a store, and that the store salesman will allow you to download software and run it on their demo computer. You could point out to them that this is well written software that does not touch the registry at all, and is very easy to uninstall without leaving any mess behind.

Otherwise, although it is a bit of a simplification, you can read up on reviews of similar computers that have the same CPU to get a feeling for their performance, particularly relative to other computer models currently available. That will give you some feeling for relativity of performance.

Generally, our strategy has always been to buy a fast state-of-the-art computer, but not the very fastest. We will happily spend an extra $100 or $200 to get a faster than 'normal' computer, with the expectation being that spending an extra few hundred dollars up front may lengthen the practical working life of the computer by possibly as much as an extra year. We would much rather pay, for example, $1250 for a computer that lasts us four years than $1000 for a computer that lasts us three years - particularly when you consider the appalling hassle involved in upgrading a computer, copying over files, reinstalling software, etc.

Lastly, to offer some advice that will quickly become out of date, it is our feeling at present (May 2010) that the 'sweet spot' of computer price/performance is represented by a computer with an Intel i7-930 CPU and 6 GB of triple channel DDR3 memory, running Windows 7 in a 64-bit version.  This will probably cost $1250-$1400 depending on options and where you buy it from.  You can expect it to score about 1650 on the testing programs mentioned above.

Is There Such a Thing as a Too Fast Computer?

Yes and no.  Some of the typical enhancements to make your computer more generally powerful and faster have little relevance to the performance you will get when using speech recognition software.  The two key areas that determine the performance you'll experience with speech recognition software are the processor speed and the amount of L2/L3 cache (this assumes that you have 4 GB or more of reasonably fast memory).

Some benchmarking studies have shown very little difference in observed user experience as between the ultimate top-of-the-line computers and those several steps down from that.  Indeed, my own experience showed less difference between an underpowered computer and a moderately powered computer than I might have expected (but possibly there were some hidden advantages caused by the more powerful computer taking more processing time to be more accurate).

So this is good news - you don't need to break the bank on getting an ultimate speed demon top-of-the-line computer.  But you also need to remember that you will be using your computer not just for speech recognition purposes.  You will probably have other programs running in the background, and so more general computing speed overall will help your computer be more productive overall.

We return back to our suggestion in the preceding section. Our feeling is that a good price performance compromise, offering you the best value, is currently represented by a computer based on an Intel i7-930 chip.

Summary of Part 3 of this Article Series

Chasing down every last partial percent of accuracy is a very valid undertaking.  There is no such thing as diminishing returns when it comes to improving the accuracy of your speech recognition system.

In this article, we also discuss the amount of processing power you need to get best use from your speech recognition software.

Coming next week will be the fourth part of our series, where we talk about how to choose the best microphone.  This one choice can have more impact on your overall performance and productivity than anything else.

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Originally published 7 May 2010, last update 21 Jul 2020

You may freely reproduce or distribute this article for noncommercial purposes as long as you give credit to me as original writer.

Related Articles
An Introduction to Speech Recognition
Is Speech Recognition Suitable for You
Accuracy and the Importance of using the best hardware

Coming next week
Choosing a Microphone
Dragon NaturallySpeaking


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