Audiometer employing narrow-band noise masking

Claim 2

In an audiometer, apparatus for generating a controlled bandwidth noise signal for selectively masking a test tone, said apparatus comprising: an oscillator for generating an essentially pure tone signal of preselectable frequency; means interconnected with said oscillator for providing a control signal which varies as a predetermined function of the frequency of said tone signal; means for generating a broadband noise signal; and means including a variable filter responsive to said control signal for modifying said broadband noise signal to provide a controlled bandwidth noise signal substantially centered on the tone frequency.

Claim 3

Apparatus as set forth in claim 1 wherein the bandwidth is substantially equal to a preselected factor times the critical bandwidth for the respective test tone frequency.

Claim 4

Apparatus as set forth in claim 2 wherein said factor is about 1.5

Claim 5

Apparatus as set forth in claim 1 wherein said oscillator provides a tone signal of substantially constant amplitude.

Claim 6

Apparatus as set forth in claim 4 wherein said control signal is a DC voltage and said control signal providing means includes a frequency weighting network to which said tone signal is applied and a rectifier operating on the frequency weighted tone signal to provide said DC control signal.

Claim 7

Apparatus as set forth in claim 1 wherein said filter comprises at least one resistance-capacitor stage in which the resistance is a light variable resistor and wherein said control signal energizes a lamp illuminating said light variable resistor.

Claim 8

Apparatus as set forth in claim 1 wherein said noise signal is initially generated at a relatively low frequency and is then transposed to the portion of the audio spectrum including the test tone frequency.

Claim 9

Apparatus as set forth in claim 7 wherein said noise signal is transposed by modulation with said tone signal.

Claim 10

In an audiometer, apparatus for generating a controlled bandwidth noise signal for selectively masking a test tone, said apparatus comprising: an oscillator for generating an essentially pure test tone signal of preselectable frequency; a variable cutoff, low pass filter; means responsive to said tone signal for generating a control signal which varies as a predetermined function of the frequency of said tone signal; means for generating a broadband noise signal and for applying said noise signal to said filter to obtain from said filter a noise sIgnal of controlled bandwidth; and means for providing a balanced modulation of said tone signal with said controlled bandwidth noise signal to generate a pair of controlled bandwidth noise sidebands centered on the tone frequency with the tone frequency being substantially suppressed.

Claim 11

In an audiometer, apparatus for generating a controlled bandwidth noise signal for selectively masking a test tone, said apparatus comprising: an oscillator for generating an essentially pure test tone signal of preselectable frequency; a variable cutoff, low pass filter; means responsive to said tone signal for generating a control signal which varies as a predetermined function of the frequency of said tone signal; means for generating a broadband noise signal and for applying said noise signal to said filter to obtain from said filter a noise sIgnal of controlled bandwidth; and means for providing a balanced modulation of said tone signal with said controlled bandwidth noise signal to generate a pair of controlled bandwidth noise sidebands centered on the tone frequency with the tone frequency being substantially suppressed.

Claim 12

Apparatus as set forth in claim 9 wherein the cutoff frequency of said filter varies substantially in proportion to said test tone frequency.

Claim 13

Apparatus as set forth in claim 9 including automatic volume control means for controlling the average amplitude of said noise signal to a substantially preselected level independent of said tone frequency.

Claim 14

In an audiometer, apparatus for generating a controlled bandwidth noise signal for selectively masking a test tone, said apparatus comprising: an oscillator for generating an essentially pure tone signal of substantially constant amplitude and of preselectable frequency; a variable-cutoff low pass filter comprising a light variable resistor and a capacitor; a frequency weighting network interconnected with said oscillator for providing from said tone signal an AC signal having an amplitude which varies as a predetermined function of the frequency of said tone signal; means for rectifying said AC signal to provide a DC control signal; a lamp for illuminating said resistor; means for energizing said lamp as a function of said DC control signal thereby to adjust the cutoff of said filter as a function of the test tone frequency; means for generating a broadband noise signal and for applying said noise signal to said filter to obtain from said filter a low frequency noise signal of controlled bandwidth; and means for providing a balanced modulation of said tone signal with said low-frequency noise signal to generate a pair of controlled bandwidth noise sidebands centered on the tone frequency with the tone frequency and the low-frequency noise signal being substantially suppressed.

Claim 15

In an audiometer, apparatus for generating a controlled bandwidth noise signal for selectively masking a test tone, said apparatus comprising: an oscillator for generating an essentially pure tone signal of substantially constant amplitude and of preselectable frequency; a variable-cutoff low pass filter comprising a light variable resistor and a capacitor; a frequency weighting network interconnected with said oscillator for providing from said tone signal an AC signal having an amplitude which varies as a predetermined function of the frequency of said tone signal; means for rectifying said AC signal to provide a DC control signal; a lamp for illuminating said resistor; means for energizing said lamp as a function of said DC control signal thereby to adjust the cutoff of said filter as a function of the test tone frequency; means for generating a broadband noise signal and for applying said noise signal to said filter to obtain from said filter a low frequency noise signal of controlled bandwidth; and means for providing a balanced modulation of said tone signal with said low-frequency noise signal to generate a pair of controlled bandwidth noise sidebands centered on the tone frequency with the tone frequency and the low-frequency noise signal being substantially suppressed.

Claim 16

In an audiometer, apparatus for generating a controlled bandwidth noise signal for selectively masking a test tone, said apparatus comprising: an oscillator for generating an essentially pure test tone signal of preselectable frequency; a variable cutoff, low pass filter; means for adjusting the cutoff of said filter as a function of the frequency selected for generation by said oscillator; and means for generating a broadband noise signal and for applying said noise signal to said filter to obtain from said filter a noise signal of controlled bandwidth; and means for providing a modulation of said tone signal with said controlled bandwidth noise signal to generate a pair of controlled bandwidth noise sidebands centered on the tone frequency.

Claim 17

In an audiometer, apparatus for generating a controlled bandwidth noise signal for selectively masking a test tone, said apparatus comprising: an oscillator for generating an essentially pure test tone signal of preselectable frequency; a variable cutoff, low pass filter; means for adjusting the cutoff of said filter as a function of the frequency selected for generation by said oscillator; and means for generating a broadband noise signal and for applying said noise signal to said filter to obtain from said filter a noise signal of controlled bandwidth; and means for providing a modulation of said tone signal with said controlled bandwidth noise signal to generate a pair of controlled bandwidth noise sidebands centered on the tone frequency.