NOMENCLATURE

It is very important that we do not insult the people we are trying to help. Deaf people do not like to be known as hearing impaired. Deaf people like to be called deaf not hearing impaired because they don’t consider themselves to be impaired people. When talking about deaf people, they prefer to be called “deaf people” and not “the deaf”. Hard of hearing people do not like to be called deaf. It’s important to realise that hard of hearing people live in the hearing world making every use of residual hearing, lip reading and facial expression and their friends tend to be both people with normal hearing and people who are hard of hearing. Deaf people tend to live in a signing world and for some of them, all their friends are deaf people who predominantly use sign language.

GENERAL

The following advice is not intended for scientists to read, it is written in an everyday language for the ordinary person. Working with hard of hearing people is enormously challenging. This is mainly because one cannot hear what they are hearing. Obviously there are no headphone sockets where you can plug in your headphones and hear what they are hearing so it has all got to be done by very sympathetic questioning and inference. The work requires great patience and empathy. Hearing aids, while technological marvels, are not the best thing for hearing music for the following reasons. Hearing aids are designed primarily for speech and not for music. Great compromises are required because of the small size of the hearing aid, battery life, and the circuitry has to work on only 3 volts. Marvellous results are obtained despite these constraints.

HEARING AIDS

Most modern hearing aids are digital but a number of people believe it would be better to be digitally controlled analogue processing but these do not seem to be currently readily available.

AN ALTERNATIVE TO HEARING AIDS

The following applies when listening to music at home along with other people and can be from any source such as television, radio, CDs and MP3s. It does not apply to listening to CDs on your own which have been specially created for you. When listening at home as above, there is no need for the constraints listed above for hearing aids and better listening results for listening at home can be obtained by using studio quality signal processing equipment which is bulky and works off the mains but can be plugged into existing home music systems or hi-fi systems. To keep down costs, we are anxious to use standard off-the shelve studio equipment which is sometimes used here in ways that designers never envisaged. One might think the most important piece of studio equipment would be a graphic equaliser to boost some frequencies and cut others but this is not so. It is more like a final step.

STEP ONE – CHOICE OF HEADPHONES

The most suitable choice of headphones are those known as “sound cancelling headphones” such as those made by Bose. Sound cancelling is an exaggeration but they partly cancel out ambient sounds so that for example if you are listening in an aircraft, the sound of the engines and the wind is partly cancelled so you can hear what you are trying to listen to, i.e. the signal being fed into the headphones, more clearly.

And thus in our application of listening to music with friends, you hear their music in an attenuated way. If you do not use sound cancelling headphones, you need to use headphones which are closed-back (so as to attenuate ambient sounds as much as possible), of good sound quality and giving loud enough sounds for the purpose. While doing the following experimentation, play some music which is at a fairly constant medium volume.

Even if you don’t like listening through headphones, follow the procedure below and then later change to small loud speakers very close to your ears. If you are going to listen without the sound in your ears being affected by the sound of the music intended for the others listening to the same music and vice versa, you will need to listen with headphones. If one ear is distorting, it would be desirable to use an ear plug if you are not using sound cancelling headphones. If you are, there should be no signal going to that ear.

When listening with others, it’s important to have your own control of the volume which means a separate headphone amplifier (almost any good quality audio amplifier will suffice; a large wattage is not needed).

STEP TWO – GETTING THE VOLUME RIGHT FOR EACH EAR

It is also important to make the best use of each ear. Sometimes what a hospital person might call the poor ear is just less sensitive but clearer for music given suitable amplification so experiment to see if this is so in your case and if so either set your music system or headphone amplifier to mono. If it does not have this facility, add the left and the right channel (this only requires two resistors and feed both to the ear which is the clearest, otherwise if both ears are reasonably clear, it enables you to use a stereo signal but adjust the relative volumes correctly) (this might be outside of the range of the balance control on the amplifier in which case two more resistors may be required and occasionally it may be necessary to use the loud speaker output rather than the headphone output to get a loud enough signal for one of the ears).

*When adding a second amplifier to an existing home music system, you will often require a pair of Y branches. These are cables about 6 inches long with a two into one arrangement of phono plugs or sockets. See photographs.

STEP THREE – KEEPING THE VALUME WITHIN A COMFORTABLE RANGE DYNAMIC RANGE AMPLITUDE COMPRESSION

Quiet passages in the music may be too low volume to be heard comfortably and loud passages can be uncomfortable or even painfully loud. Painfully loud we want to avoid at all costs. What we need then is to automatically turn up the volume in quiet passages and turn it down in loud passages and also frequency discrimination is poorer if the volume gets too high, e.g above 80 dBHL, so it is always best to err on the side of less loud. The studio quality device that can do this is called a dynamic range amplitude compressor. This device, and not the graphic equaliser, is the most important single item after step two from all the studio equipment to help people with hearing impairments. What a dynamic range compressor does is shown in figure 1 and as you will see after a fresh hold level for the volume is reached, a smaller increase in output is given for a given increase in input. The ratio between these is called the compression ratio which can be dialled on the front panel. There are also settings on the front panel for timing response because the compressor cannot act instantaneously but for automatic gain control, these should be set to a “slow response setting”. In other words, this is dynamic range compression set up for automatic volume control. A compression ratio of about 3 should be suitable. If stereo listening is in operation, a stereo compressor should be used and the same settings should be used on both channels. Some compressors have a switch on the front panel to enforce this.

STEP FOUR – FAST ACTING DYNAMIC RANGE COMPRESSION

This compressor should be a separate unit connected after the unit above. Most of the time in classical, and similar music, it will do nothing “but it earns its keep” by catching any sudden loud notes and turning the volume of these down so as to avoid the listener being subjected to painfully loud music at all costs. If you were sure that the source material after being compressed as above will not contain any exceptionally loud notes, it may not be necessary. In music which is varying in volume very rapidly, i.e loud and soft notes in quick succession, it is complicated to set up the fast acting compressor and it wouldn’t be worth while learning how to do this as a one-off so I suggest you ask an expert to do it as a one-off job. It’s important not only to avoid loud notes coming through but also to avoid “pumping sounds”.

If you are only using mono, you can save money by using the unused side of the compressor of three of a second compressor as the compressor for number 4. Be sure the input signal into the fast acting compressor is not too high, otherwise distortion will occur.

STEP FIVE – SELECTIVE COMPRESSION

The above is all that is normally required for compression but if you wish you could experiment with the following. Sometimes people are bothered by very loud low notes or alternatively high notes. And if that is the case, you might like to experiment as follows. Use a graphic equaliser to select either low notes or high notes and feed this signal into the control input of the first dynamic range compressor. A simple graphic equaliser will be adequate for this purpose. I would advise against trying to split the sole signal into different frequency bands and compressing each band differently. The reason being this produces too much change in timbre and can produce other disorientating effects. This opinion is backed up by other researchers at Keele University where I worked as a visiting fellow.

STEP SIX – EQUALISATION

We wish the listener to hear notes right across the frequency spectrum used in music equally loudly or, at the very least, across the range of pitches used in the piano (which is a wider frequency range than you might think because there are many higher harmonics on the upper range of notes on the piano) so this means boosting some frequencies and cutting others. To get adequate control and selectivity, a 30 band graphic equaliser should be used such as an ALESIS M-EQ 230 with the left and right channel adjusted individually for each ear. Before boosting certain frequencies, bear in mind that there may be distortion at some frequencies. For example, the ear is most sensitive at about 2.5 kHz and people who have been subjected to industrial noise often have distorted sound around that frequency. In many cases, where noise damage has occurred, it may be desirable to cut rather than boost the amplitude at around 2.5kHz or at any frequency where noise damage has occurred. Experimentation is required preferably using a signal generator which can either be a hardware one or an app as available on an iPod or similar. Bear in mind that it is absolutely pointless boosting frequencies where there is no hearing; all that one will achieve is generating noise. If for example, the highest frequency a listener can hear is 7 kHz, it may well be worth boosting 7 kHz in the hope that 8 kHz can be heard to some extent but absolutely pointless to boost 10 kHz and above. At the bass end, if loud bass notes are causing a problem even after the equalisation, it may be expedient to cut down their amplitude but this should really be tackled on the compression stage. I have never found it worthwhile to use two graphic equalisers in succession. It just creates noise but if you do try it, be sure that the signal from the first equaliser is not so high in amplitude that it overloads the second which would cause severe distortion.

LISTENING TO SPECIAL RECORDINGS

COMMERCIALLY AVAILABLE RECORDINGS

These could be listened to on your own or with friends and family. An example of recordings which are much clearer than the original are arrangements of Mozart’s operas for wind band by for example Joseph Trebeze. These maintain the essence of the music but are much clearer with fewer musical parts and, because of the contrasting timbers, the parts are much easier to pick out. These arrangements are enjoyed by many people not just hard of hearing for which they were never intended. Wind bands played these commonly in the street in Mozart’s time. I collect arrangements which are clearer for hard of hearing people and I suggest you ask your family and friends to do the same. Original pieces which have contrasting instruments for example quintets for piano and winds rather than string quintets / quotets can be easier to listen to for the same reason.

SPECIALLY MADE RECORDINGS

Some of Bach’s music, e.g Fuges, is difficult to appreciate because it’s hard to pick out the individual parts because they are all played with a similar timber. So if you can get a few friends to play the parts with contrasting instruments, this can sometimes be much clearer.

COMPUTER GENERATED MUSIC

Computer generation allows vast control, for example you can move some or all parts by octaves and choose the instruments (timbers). This advantage is that unless you spend an enormous amount of time and energy, the performances are never very expressive. And are absolutely never as expressive as those of top performers. An example of how you can manipulate the music is to put small detachment gaps between notes so that the sound of one note dies away before the next note begins. In musical terms, this would correspond to playing slightly staccato and this is an example of one of many many things that you can try when working with very hard of hearing people. Another example is doubling of musical parts, for example if you have an organ sound where the amplitudes rises relatively slowly it can be useful to double it with a harpsichord sound which gives a very clear start to the note. Another example is timbers which die away very quickly and can have their amplitude envelope extended which makes pitch perception easier.

You can also do arrangements, for example in a Fuge you could set it with four contrasting instruments. You could also try spatial separation by having each of the instruments come from a separate loud speaker placed around the room or if you are using a vibro acoustic chair (see you later) each instrument sent to a different vibration unit on the chair, so that for example you might hear an oboe type sound on your left back and a clarinet sound on your right back, cello on your seat and a plucked double bass on your feet. You can adjust the volume of each instrument individually so you can achieve a good balance allowing for the fact that the listener might not hear an oboe sound as loudly as a clarinet sound or vice versa. Preventing parts crossing with octave shifts is another example. An octave shift of the whole thing can be useful in that some people can hear better higher or lower but if transposing down by octaves be aware that the sound can become “muddy”. This is an inevitable consequence of acoustics. If you have a piece with rapidly alternating loud and soft notes (remember this was difficult to deal with with an analogue dynamic range compressor) you can produce a new version of the piece processing it digitally with software such as Audacity which is available free of charge. But be aware, this cannot is not in real time listening.

VISTA MUSIC

This is software I developed standing for visual and tactile music. This is the name I gave to software I developed myself for people who were going extremely deaf. It contained features for all the above in a convenient form. It also had especially good facilities for creating expressive performances.