AUTOMATIC LOUDNESS CONTROLLER

• US 3,582,964 A
• Filed: 09/30/1968
• Issued: 06/01/1971
• Est. Priority Date: 09/30/1968
• Status: Expired due to Term

• Current Assignee: Allan J. Rosenheck, Benjamin B. Bauer, Emil L. Torick, Richard G. Allen
• Original Assignee: Allan J. Rosenheck, Benjamin B. Bauer, Emil L. Torick, Richard G. Allen
• Inventors: Torick, Emil L., Allen, Richard G., Bauer, Benjamin B., Rosenheck, Allan J.
• Application Number:
  US04/763,897
• Time in Patent Office: 974 Days
• US Class Current: 381/103
• CPC Class Codes: H03G 9/14 for gain control and tone control

Abstract

In the particular embodiment of the invention described herein, program signals are supplied to a unity gain amplifier. An analysis of program loudness is made by equalizing the signals in accordance with a selected ear sensitivity response characteristic. A plurality of band-pass filters divide the equalized signals and the divided signals are first rectified and then combined linearly by a combining network. The combined signal is then supplied to a ballistics shaping network which simulates the ballistic characteristic of the human ear. The resulting control signal is then supplied to a variable gain stage of the unity gain amplifier to vary the gain of the amplifier to control thereby the loudness level of the program material.

Claims

1. Apparatus for automatically controlling the loudness levels of broadcasting sounds comprising amplifier means adapted to amplify linearly signals corresponding to broadcasting sounds and loudness analyzer means responsive to the signals amplified by the amplifier means and adapted to control the gain of the amplifier means in accordance with the loudness levels of the broadcasting sounds, the loudness analyzer means comprising equalizing circuit means having a transfer function inversely proportional to an equal loudness contour over the range of loudness levels of broadcasting sounds represented by said signals, separating means for separating the equalized signals into a predetermined number of frequency bands, a corresponding number of rectifying means for individually rectifying the separated signals and means for arithmetically summing the rectified signals to produce a control signal and for supplying the control signal to the amplifier means to control thereby the gain of the amplifier means.

2. Apparatus according to claim 1 wherein the amplifier means comprises a unity gain amplifier including a variable gain stage responsive to the control signal for controlling the gain of the amplifier.

3. Apparatus according to claim 2 wherein the loudness analyzer means further comprises circuit means interposed between the summing means and the variable gain stage of the unity gain amplifier operative to shape the control signal to conform the response of the apparatus with the response of the human hearing process to impulsive sounds.

4. Apparatus according to claim 3 wherein the rectifying means include means operative to linearize the rectified signals whereby the amplitudes of the output signals from said rectifying means are linearly proportional to the amplitudes of their respective separated signals.

5. Apparatus according to claim 4 wherein the loudness analyzer means further comprises variable threshold adjustment means responsive to the signals amplified by the unity gain amplifier for controlling the operation of the loudness analyzer means and means for limiting the gain reduction over a range corresponding to the average loudness level variations of the broadcasting sounds.

6. Apparatus according to claim 5 wherein the separating means comprises a plurality of filters for dividing the equalized signals into frequency bands of from about 50 to 500 Hz., 500 to 1000 Hz., 1000 to 2000 Hz., 2000 to 4000 Hz., and 4000 to 15000 Hz., respectively.

7. Apparatus according to claim 5 wherein the equalizing circuit means has a transfer function inversely proportional to a 70 phon equal loudness contour representative of the loudness levels of broadcasting sounds as a function of frequency and intensity over a range of pressure levels from about 60db. to about 80db.

8. Apparatus according to claim 5 wherein the loudness analyzer means comprises means for limiting the gain reduction of the unity gain amplifier to a maximum of 6db.