An audiometer that automatically produces test tones of predetermined duration whose frequency and level are changed in accordance with a programme. The persons being examined actuate a switch or the like each time that a test tone is perceived and the parameters of said test tone (frequency and level) are stored in a memory. Thus, evaluation becomes very simple. Furthermore, steps have been taken to measure the background level in the test room and to ensure that the test tone is repeated when the background level exceeds a maximum value during the time that the test tone is produced.

The invention relates to an audiometer which automatically generates a 
series of test tones of predetermined duration, different frequency and/or 
different levels in accordance with a programme. The audiometer also has 
one or more test stations which each comprise a reproducing device and an 
actuating element for recording the test tones which have been perceived. 
Such an audiometer is known from United Kingdom Pat. No. 1,348,197. During 
a predetermined time interval (=presentation time) this audiometer 
produces a test tone whose frequency and level are constant during the 
presentation time. This tone is presented to all of the reproducing 
devices (headphones) at the same time. When the test tone is perceived, 
the subject actuates a push-button which initiates a recording operation 
for the relevant test station and for the relevant test tone. After a 
pause a different test tone with the same presentation time but with a 
different frequency and/or different level is produced so that at the end 
of the examination procedure the ability to hear can be determined on the 
basis of a series of test tones each time of a different frequency and/or 
different level. 
The test tones being perceived are recorded by means of a so-called stylus 
unit. This stylus unit has a stylus for each test position, upon whose 
actuation the tone which is then perceived is marked in an audiogram 
corresponding to the test station. In this audiogram the level of the test 
tone being perceived is plotted as the ordinate and its frequency as the 
abscissa. For a new test tone of a different level the stylus unit is 
bodily moved in the direction of the abscissa of the audiogram chart (for 
a test tone of a different frequency it is moved in the direction of the 
ordinate) so that the individual styli are then each positioned above that 
point of the associated audiogram chart which is representative of the 
level and the frequency of the test tone. 
The stylus unit is a complicated vulnerable part of the audiometer. 
Extension of the number of test stations is possible, but only with 
considerable difficulty. Evaluation of the large number of audiogram 
charts employed for a series examination with such an audiometer is 
time-consuming. 
It is an object of the invention to provide an audiometer which is less 
vulnerable, which is more flexible with respect to the number of test 
stations, and which simplifies the evaluation procedure. 
According to the invention this problem is solved, starting from an 
audiometer of the type mentioned in the preamble by providing a digital 
electronic memory or a part of such a memory having a write input or an 
information input allocated to each test station. A digital signal 
corresponding to the level or frequency of the test tone is applied to the 
information and/or the address inputs of the memory. The memory write or 
information input associated with a test station can be controlled by the 
actuating element located at the test station and an output device is 
provided for the read-out of the signals stored in the memories or the 
memory. 
Storage is possible in different ways: 
(a) To the information input a digital signal is applied which corresponds 
to the frequency and the level of a test tone. The write input can be 
controlled by the actuating element so that the digital signal which 
appears on the information input is stored when the subject perceives the 
test tone and actuates the actuating element. 
(b) To the address input of a memory an address is applied which 
corresponds to a test tone parameter to be changed, preferably the 
frequency, and to the information input a digital signal is applied which 
corresponds to the other parameter, i.e. the test tone level. When the 
subject perceives the test tone and operates the actuating element, the 
test tone level is written into the memory in the address assigned to the 
test tone frequency. This write-in method requires a low storage capacity 
and renders satisfactory evaluation possible. 
(c) A digital signal, which characterizes the level and frequency of the 
test tone, is applied to the address input only. The actuating elements 
should then be connected to the information inputs of the digital memory. 
When they are actuated by the subject a binary signal ("1" or "0") is 
written into the memory in the address corresponding to the frequency and 
the level of the test tone. 
The use of digital signals which characterize the test tone frequency and 
level constitutes no significant additional complication because such 
signals must be available anyway for controlling the frequency and the 
attenuation or gain of the tone generator. 
Audiograms thus obtained can be evaluated automatically in a particularly 
simple manner. As an example, the hearing thresholds thus determined for 
the different frequencies may be compared with the (equally stored) 
"normal values" for a person of the same age, and--in addition to the 
absolute values--the difference in level between the thresholds of hearing 
of the subject and a person with normal hearing can be read out with the 
output device, for example, a printer. 
For audiometric measurements correctly sound-proofed rooms are necessary, 
which in virtually all cases can be realized only with substantial cost. 
In the case of mobile devices, for which the audiometer in accordance with 
the invention is particularly suitable, this is particularly difficult or 
in many cases impossible for reasons of bulk and weight. Despite the use 
of acoustic caps which damp extraneous sounds, it may therefore frequently 
happen that audiometric test results are invalidated by background noise 
because the subjects do not hear the test tone when there is background 
noise or mistake the background noise for the test tone to be perceived. 
In accordance with a further embodiment of the invention these erroneous 
results can be avoided in that the test room is provided with a microphone 
for measuring extraneous sound, means are provided for the formation of a 
signal which corresponds to the average value of the microphone signal 
level during the presentation time of the test tone, and that depending on 
the difference in level between the extraneous sound and the test tone the 
test tone can be repeated. The signal which then causes the test tone to 
be repeated may then simultaneously suppress the signal produced by the 
actuating elements or may cancel the values stored in the memory during 
the extraneous sound so as to prevent any incorrect results. 
Instantaneously occurring extraneous sound effects, which mask a test tone 
which has just been given, thus cause the test tone to be repeated, namely 
a predetermined number of times or so often that the difference in level 
between the test tone and the room level has reached a permissible value. 
The permissible value of the difference between the test tone level and 
the extraneous sound level depends on the quality of the acoustic caps 
fitted around the headphones and may be adjusted in accordance with their 
acoustic damping values. An audiometer thus equipped may then also be 
employed in less satisfactorily sound-proofed rooms.

The invention and further advantages thereof now will be described in more 
detail with reference to the drawing. 
The tone generator comprises an oscillator 1 with a frequency which is 
adjustable in steps. The oscillator output signal is applied to a switch 3 
via an amplifier 2 whose gain or attenuation is electronically adjustable 
in steps. The opening time of said switch determines the intervals between 
two test tones and the closing time corresponds to the duration of a test 
tone, i.e. the presentation time. The output of the switch 3 is connected 
to a plurality of headphones 25 via a change-over switch 4, via which 
headphones--depending on the position of the switch 4--the test tone can 
be applied at option to the left or the right or both ears of the subject. 
The oscillator 1, the amplifier 2, the switch 3 and the change-over switch 
4 are controlled by a converter 5, which in its turn receives instructions 
from a programme control unit 6 via the line 65 and supplies information 
to the programme control unit via the line 56. For controlling the 
oscillator 1 and the attenuation of the amplifier 2 the converter 5, in 
known manner, may comprise a shift-register with a number of register 
cells corresponding to the number of frequency and damping stages 
respectively (compare United Kingdom Pat. No. 1,348,197). However, there 
may also be provided a coding device which re-codes the, for example, 
binary-coded signal supplied by the programme control unit 6 and 
corresponding to the test-tone frequency and level in such a way that only 
one of its outputs, whose number corresponds to the number of frequency 
and level stages respectively, carries a specific digital signal ("1" or 
"0") and renders a resistor in the oscillator 1 or amplifier 2, which 
resistor determines the frequency or level respectively, operative. In 
addition to the headphones 25 the test stations 7--the drawing shows only 
three stations but there may be provided any arbitrary number of other 
stations--each comprise an actuating element in the form of a key switch 8 
to be actuated by the subject being tested when a test tone is perceived. 
So far the audiometer is essentially similar to the device shown in the 
aforesaid United Kingdom patent. 
The switches 8 are each connected to the write inputs of memories 10 via an 
AND-circuit 9. The information inputs of the memories 10 are connected to 
the programme control unit 6 via line 11 and their address inputs via line 
12. Via the line 11 the programme control unit supplies an information 
signal which characterizes the instantaneous level of the test tone and 
via the line 12 an address signal which characterizes the instantaneous 
frequency of the test tone. For the sake of simplicity the drawing shows 
only one information line 11 and one address line 12, but in practice more 
lines are required. These signals are also applied to the converter 5 
which changes the level and the frequency accordingly. If a switch 8 is 
actuated by one of the subjects when a test tone is perceived, the 
information signal characterizing the test tone level on the line 11 is 
stored in the memory 10 associated with the actuated switch at the address 
determined via the line 12 and characterizing the frequency (and the ear 
being examined--right, left). 
Storage of the test tones which have been perceived may also be effected as 
described in the introduction under (a) or (c). It is essential only that 
the values stored in the memory 10 unambiguously correspond to the 
frequency and the level of each test tone being perceived. Instead of a 
separate memory for each test station there may also be provided a common 
memory for all test stations. The output signals of the AND-circuits 9 
should then be stored temporarily and read out sequentially. 
The outputs of the memories 10 are connected to an output device, for 
example in the form of a printer 13, and the results can be printed--time 
sequentially--on said printer. The programme control unit 6, the memories 
10, the functions of the gates 9 and the printer may be realized jointly 
by means of a commercially available calculator. The programme control 
unit 6, however, can also be designed on the basis of a microprocessor, 
which can then also perform the functions of the AND-gates 9. 
If one of the switches 8 is not actuated during a test tone (i.e. if the 
switch remains open) or after a specific comparatively short time interval 
after the test tone has been produced, but later, before the next tone is 
produced, it may be assumed that the subject has not perceived the test 
tone although the switch 8 has been actuated. In order to prevent storage 
of this test tone a signal may be applied via a line 14, which signal 
blocks all AND-gates for a specific time after each test tone has been 
produced and does not release them until the next test tone is produced. 
This signal may for example be generated by the converter 5 which switches 
the test tone on and off. However, instead of this, write instructions 
which arrive too late (i.e. a specific time after the test tone has 
sounded) may be added to the contents of another storage location in the 
relevent memory, for which purpose the signals on the address and the 
information inputs of the memories should also be changed during these 
time intervals. The contents of this storage location at the end of an 
audiometric test then indicates how many times the subject has responded 
incorrectly. 
When the test room is not satisfactorily sound-proofed, in particular when 
a large number of persons are examined in said room at the same time, it 
may happen that a test tone is masked by extraneous sound or that the 
subject erroneously takes the extraneous sound for the test tone. Such 
erroneous responses cannot be entirely prevented by acoustic caps which 
are mounted over the measuring headphones 25 because the acoustic damping 
values are naturally limited. 
Therefore, in accordance with the invention, an average value of the 
extraneous sounds during the presentation time of a test tone is formed, 
and the test tone is repeated when the difference between the level of the 
test tone and the extraneous sound exceeds a predetermined value--which 
preferably depends on the damping values of the acoustic caps--(i.e. when 
the sound pressure of the test tone is a specific factor greater or 
smaller than the sound pressure of the extraneous sound). For this purpose 
there is provided a microphone 15 whose signal is amplified by an 
amplifier 16, which preferably has a variable gain, and applied to a 
filter 17 whose frequency response substantially corresponds to the 
frequency response of the hearing of a person with normal hearing. The 
output signal of this weighting filter 17 is rectified in a rectifier 18 
and applied to a frequency converter 19, whose output signal has a 
frequency which is proportional to the amplitude of its input signal. The 
output pulses of converter 19 are counted by a counter, not shown, in the 
converter 5 during the presentation time, i.e. while the switch 3 is 
closed. Thus, the count at the end of the presentation time is a measure 
of the extraneous sound during the presentation time. When the difference 
between the extraneous sound thus measured and the test-tone level 
determined by the programme control unit via the line 65 exceeds a 
predetermined value, the programme control unit is made to repeat the 
instruction associated with said test tone via the line 56. The test tone 
may then be repeated a predetermined number of times or until the 
difference between the test tone and the extraneous sound has reached a 
permissible value. Suitably, the contents of the storage location 
corresponding to the test tone is then erased in order to avoid incorrect 
registrations. It is alternatively possible to measure the background 
level outside the presentation time of the test tone and to repeat the 
measurement until the difference between the extraneous sound level and 
the test tone level exceeds the predetermined value, after which the test 
tone--by closure of the switch--is presented to the subject. Preferably, 
the two possibilities are combined. Thus, when the background level during 
the measurement is too high, the extraneous sound measurement is repeated 
until the measured background level has decreased to the permissible value 
and it is not until then that the test tone is repeated. The interruption 
of the series of test tones, which are preferably produced at variable 
time intervals, in the case that the permissible background level is 
exceeded may be signalled to the subjects by optical or other signals. 
It is not necessary to convert the extraneous sound level into a digital 
signal whose frequency depends on the level. It is for example possible to 
vary the gain of the amplifier 16 by means of the converter in a sense 
opposed to that of the gain of the amplifier 2 so that the product of the 
two gain factors remains constant. In this case an extraneous sound level, 
which bears a specific ratio to the effective-signal level, results in a 
direct voltage at the output of the rectifier 18 which is independent of 
the effective-signal level. Whether said threshold value is exceeded can 
simply be detected by means of a threshold switch. Similarly, a signal 
which is proportional to the amplitude of the output signal of the 
amplifier 2 may be compared with the output signal of the rectifier 18 and 
the test tone may be repeated when the output signal of the rectifier 18 
is predominant.