Microphones for Speech Recognition
Introduction
When used in a quiet environment, many of the cheap microphones supplied with voice recognition software packages work well enough to demonstrate the potential of speech recognition. However, we recommend that you purchase a high quality microphone for greater durability and to obtain best results from your software.
The best results for speech recognition are gained when the microphone is kept a consistent distance from your mouth. For this reason we recommend headset microphones for dictating to your PC. If you are using a portable dictation machine or a MiniDisc recorder you may want to use a stub microphone which we will deal with at the end of this article.
Contents
Which Microphone Should I Use?
We would recommend using the following;
- A noise-cancelling microphone (which samples background noise and filters it out);
as these are less likely to be affected by noises other than your voice, and consequently give better results.
Each user will have different likes, dislikes and reasons for choosing one microphone in preference to another; a frequent factor in microphone choice is comfort. It is entirely dependent on the shape of your head which microphone you find most comfortable.
Testing Methodology
We test a wide variety of microphones on a range of different computer systems and with both the current market leaders in speech recognition software, Dragon NaturallySpeaking and IBM Via Voice (please note that at the time of this update, July 2006, Via Voice is not compatible with Tiger 10.4.6, but will work on earlier Mac OS):
- We try to keep our testing standardised to ensure that results are as accurate as possible.
- For each system and each different microphone we do a general check of the microphone using the audio set up wizard, and then follow the basic enrolment procedure.
- We then dictate a standardised text into the application’s word processor and also into Microsoft Word, and note the number of mistakes.
- Then we correct the dictation, save the user files, repeat the process and note the results again.
Results
The following Headset Microphone gave good results during testing:
Andrea Electronics (Active Noise Cancelling) NC91
The Andrea Electronics NC91 uses noise cancellation. It has a flexible microphone boom, and a comfortable earpiece with stainless steel adjustable headband which is suitable for those with a larger head.
USB Pods
USB pods contain their own electronics, and as a consequence they may give better results than some internal soundcards (especially in laptops when the soundcards may be located close to the hard drive or the system fan which may adversely affect recognition).
For satisfactory results with USB pods such as the Andrea USB Pod we recommend at least Windows 98 second edition, Windows 2000, Windows ME, or Windows XP.
Even then, we do not recommend using a USB pod if you are using other USB devices on your computer at the same time. This is because USB devices take their power from the USB connection. Connecting too many devices simultaneously will result in not enough power being delivered to each device and as a consequence recognition performance can suffer.
Earlier problems with drop-outs have not been encountered during testing; however, this may be due to the fact that in the time that has elapsed since we last wrote about microphone performance, personal computers have increased in power dramatically.
Another advantage of using a USB pod is that you can connect any microphone you choose to any computer with a USB port. We got satisfactory results from various microphones when using the Andrea Electronics USB adapter.
Stub Microphones
These give better sound quality, and therefore better recognition, than built-in microphones in portable note-takers like the Dragon Mobile / Voice IT recorder and the Olympus DS 150. The Sony ECM-DS70P is a reasonably priced stereo microphone suited to lecture theatres. You will also need a microphone if you are using a MiniDisc recorder. You can use a headset microphone such as the Andrea, although you may find a stub microphone more convenient and more suited to the pocket nature of your recorder.
