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World’s first digital voice amplifier

An analogue amplifier distorts the voice. A digital amplifier reproduces the voice as it is normally spoken, and the listener hears the natural voice. A person who uses a digital voice amplifier thus recognises his or her own voice.

The properties of the voice are dependent on anatomical structure and how the voice is used. It is possible to change voice behaviour. This requires training and yet more training.
Teachers are the professional group who most often seek medical help for voice problems. This is because they use their voices daily to speak to groups in various environments and situations.

Most patients who consult a doctor or speech therapist with the diagnosis of voice fatigue are women. Women’s voices are lighter and weaker than men's voices. Therefore, women raise their voices in order to be heard. Apart from being lighter, the female voice does not have as close overtones as the male voice, and this is one of several reasons why women’s voices are more difficult to understand in some acoustic environments.

The vocal chords of a woman teacher vibrate more than one million times during a normal work day if she talks 20 percent of the time – but a male teacher’s vocal chords only vibrate half a million times. A man’s voice has an average of 100 vibrations per second (a frequency of about 100 Hz) but a woman’s vocal chords, which are much shorter, vibrate roughly twice as fast.

Doctoral research indicates that a person who speaks in a compelling way gets the attention of the listener and is perceived as interesting, compared with a person who has voice problems and difficulty in putting over the message. Therefore, it is important that one's voice should be reproduced as clearly and as well as possible. Analogue reproduction never reproduces the voice correctly, but digital amplification and reproduction do.

The Swedish Teachers' Union states the following in its publication, “Your voice is your most important tool”:

“In most groups diagnosed with voice problems, women constitute the majority. The most common diagnosis is phonasthenia, i.e., voice fatigue. In phonasthenia, common symptoms are a feeling of irritation and pain in the neck. The sufferer clears his or her throat often and sometimes the voice becomes unstable. It is difficult to speak more loudly, but above all, the voice feels tired. The voice is often monotonous and creaky. But a person whose voice sounds rather good can also have phonasthenia and experience severe problems.”

Voice fatigue, i.e. phonasthenia, can be prevented by using a digital voice amplifier which relieves pressure on the voice. As soon as your voice begins to feel strained, you should connect up the digital voice amplifier. This makes you feel better, and the message you are putting over reaches the group you are talking to. If you continue to strain your voice without relief, surveys have shown that this often leads to complaints about dry, stagnant air, dust, dirt and noise, while experiencing symptoms such as tiredness, dry throat and hoarseness. The consequences are demands for expensive rebuilding and time off sick. Therefore an employer has a lot to gain by helping personnel who have problems or who have to strain their voices.

Digital reproduction
With analogue amplification, the voice becomes distorted. With digital amplification, the voice is reproduced and perceived as it is normally spoken. A person who uses a digital voice amplifier thus recognises his or her own voice.

The output power of Voxema’s voice amplifier is at least twice as good as any analogue voice amplifier on the world market. This is thanks to the digital program which we designed. The program has the following advantages:
- Removes unnecessary smacking sounds and gives a clearer, more powerful sound.
- “Compresses” the sound in even amplification throughout the entire frequency range from 0 to 14 000 Hz.
- Creates a reward system which automatically shuts off the voice amplifier for a few seconds if you speak too loudly (to prevent you straining your voice unnecessarily).
- Eliminates all acoustic feedback and creates a filtering system which makes clearer speech.
- The program has two levels for different environments and voice situations. Can easily be switched to the situation you happen to be in.
- The program in the voice amplifier adjusts to the voice or voice problem.

The items listed above are some of the things that a digital program in a voice amplifier can achieve compared to an analogue voice amplifier. The program can be continually improved with various filtering systems and more sensitive microphones, which can be adapted for various environments and situations. Soon it will also be possible to transmit speech from the digital voice amplifier by wireless (Blue Tooth). This means that mobile telephones will be able to receive and transmit speech in an ongoing conversation. This will be a considerable improvement for many people who have voice problems. Speech in mobile telephones will be clearer and better.

A DSP or signal processor is a processor which is specially adapted for processing signals. Such processors are found in many types of apparatus in which signals need to be processed. For example, mobile telephones, network cards, CD players, etc. DSP processors are designed specifically for the tasks they are intended to solve, and are much faster for this than normal CPUs, but are slower at other things.

Tasks which are suitable for a DSP are:

FFT - Fast Fourier transforming
Filtering of sound, among other things
Advanced bit manipulation
CRC calculations

Application of DSP for digital voice amplifier:
Signal processors can be used as sound processors and built into amplifiers, bases and other HiFi equipment, and in combination with advanced software, can be used to adjust the character of the sound without impairing the quality of the sound. This has only become possible in recent years thanks to high resolution digital technology. This is the main reason why Voxema has chosen to use digital technology in the product.

It would be utopian to try to define an absolute optimal sound reference, because there is always individual personal taste as reference in the search for the “perfect” sound, and it is always a subjective assessment. Consequently there is also considerable variation as regards what types of sound are preferred. The DSP technology allows sound to be adjusted exactly, so that it sounds “perfect” in your ears.

Practical applications made possible by digital technology for Voxema’s voice amplifier:
The voice amplifier must have various types of filter in order to be able to maintain the sound quality that Voxema aims for.

Sound filter
This filter must be able to filter away several types of sound, such as smacking sounds, wheezy sounds, scraping sounds, wind, noise, etc.

Disturbance filter
This filter is intended to filter out disturbing sounds which come from mobile phones or other electrical equipment which can cause disturbance.

Volume, Stick & Carrot
The voice amplifier has stepless volume control, which is suited for various environments, for example, indoors, office, meetings, outdoors, in town, large crowds, the pub, etc., to permit normal conversation. Inbuilt into it is a stick and carrot system. When you speak or whisper too loudly in relation to your voice, it “punishes” you by shutting down for a few seconds. You learn to increase the volume of the voice amplifier instead of raising your voice. The reward is a less stressed voice.

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