For anyone involved in the sound recording industry, good hearing is essential. Yet typical medical tests only check for hearing losses greater than 30dB below 8kHz! However, Digital Recordings have produced a handy self‑assessment CD which allows musicians to more accurately monitor their own hearing acuity over time.
The CD is provided with comprehensive instructions and is very straightforward to use. The first check is to determine the suitability of the CD player with a specially designed low‑frequency, low‑level test tone. If any clicks are heard during its replay, the CD player is not replaying the tone correctly and the machine is therefore not adequate for the hearing test. If all is well, the next stage is to 'calibrate' the replay level through the headphones, although it should be remembered that this, and all subsequent, tests will be affected by the frequency response, noise floor and linearity of the equipment used. Digital Recordings recommend the use of the AKG K270 headphones, although any high‑quality ones should provide acceptable results (I used K240 open‑backed headphones in a very quiet room). You should also use the best headphone amplifier available to you — the built‑in headphone amps in many CD players are not always particularly quiet!
The level calibration signal consists of an alternating sequence of high and low frequency tones and the replay level is adjusted until these can just be perceived. The notes recommend having this calibration performed independently by a number of different people (including children) and the lowest value used. Clearly, if it is determined by someone already suffering a degree of hearing impairment, the results will be inaccurate. If set correctly, the maximum replay level through the rest of the tests should not exceed 80dBA, which is well within the safe range of listening levels.
The hearing test proper occupies 24 tracks of the CD, each carrying a different frequency tone (left channel only), at a level which rises over an 80dB range. The listener simply notes the track time when the tone becomes audible. Once all the tracks have been auditioned, the headphones are reversed and the entire sequence replayed for the right ear, thereby ensuring that any disparity between left and right signal paths is irrelevant. The timer readings for each ear can then be plotted on a chart within the accompanying booklet. Results within ±10dB of the ideal curve shown on the chart are considered normal.
While this hearing test isn't 'laboratory standard' — the system relies on the accuracy of the user's CD player and headphones — my own results proved remarkably consistent between three separate tests spaced over several months. I can thoroughly recommend Audio‑CD as a self‑administered hearing test, in some ways exceeding the standard capabilities of normal 'medical' hearing tests. Although not of interest or practical use to everyone, those with a specific interest in their hearing acuity will find this disc invaluable.