Method and Apparatus for Signaling the Volume Level of Reproducing Apparatus for Digitally Recorded Sound

1. Field of the Invention

This invention relates to digital records of audio performances and to player apparatus for reproducing the sound performances from the records, and to a method and apparatus for generating audio warning signals prior to the start of reproduction of each performance.

2. Prior Art

If the volume control of a phonograph is set too high before the reproduction of the recorded musical performance begins, the listener may be subjected to an uncomfortably high level of sound when the performance starts. If earphones are used, these sounds can damage the listeners eardrums. When a conventional phonograph record is played, the background noise generated by the record at the leading edge, prior to the start of the performance, generates a warning signal to the listener so that an excessively high setting of the volume control can be detected before the performance starts and the volume control can be lowered to a more appropriate level.

This background noise level produces a hiss on reproduction throughout the performance. Removal of this background noise level is one of the advantages provided by systems which record the sound performance in digital form, usually on record media consisting of laser readable disks or magnetic tape, and employ a digital player to reproduce the performance stored on the record media. The absence of random background noise during the reproduction of the performance is an unalloyed benefit, substantially improving the quality of the reproduction, and the silence due to the absence of background hiss before the reproduction of the first recorded sound performance on the media and between sequential performances on the same record, conveys to the listener an impression of the high quality of the reproduction process.

But that very silence creates a problem with prior art digital record players for those recordings, in that the listener receives no audible signal as to the setting of the volume control of the player, and if the volume control is set too high, the actual musical performance may begin with an unpleasant or even dangerous blast of sound. The danger is particularly acute if the listener is using earphones and can result in temporary or even permanent loss of hearing.

The present invention is accordingly directed toward a method of generating warning tones prior to the playback of digital recordings with the warning sounds having a substantially lower amplitude than the sound performance to be reproduced. The volume of the warning sound provides the listener with an audible indication of the setting of the volume control for the player without itself constituting a dangerously loud sound. The method of the present invention may be practiced by either digitally recording low amplitude warning signals on digital recordings before the encoding for each performance so that when the sound is reproduced using a conventional record player a warning signal is generated which is lower in amplitude than the ensuing performance, and has an amplitude that is a function of the volume control setting; or, alternatively, providing a record player that may be used with conventional digital records but contains circuitry for generating the desired warning sound for a few seconds before commencing reproduction of the sound signals recorded on the record. This latter arrangement has the advantage of generating the warning signal even if the player is controlled to begin reproduction in the middle of a recorded soundtrack. This arrangement has the further advantage in that it may include circuitry which allows the listener to disable the warning signal.

With either embodiment of the apparatus for practicing the invention, a warning sound may be generated in such a way as to produce a short period of silence before the warning tone to convey to the listener the purity of the reproduction process.

The warning sound may take the sound of a tone, either continuous or interrupted, or a particular musical sound such as bells, trumpets or the like. The period of the warning sound should be sufficient to allow the listener to adjust the volume control before the start of the ensuing performance, and may be in the range of 2-10 seconds.

Other objectives, advantages, and applications of the present invention will be made apparent by the following detailed description of several preferred embodiments of the invention.

The description makes reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a digital recording on a disk and a player for the recording of the type useful with the present invention;

FIG. 2 is a plot of the amplitude of sound signals produced by a digital record containing a number of musical performance, each preceded by a warning sound generated by digital coding on the record media;

FIG. 3 is a schematic diagram of the circuitry of a digital record player incorporating means for generating the warning sounds of the present invention when used with conventional records; and

FIG. 4 is a plot of the amplitude of sound signals produced by the player of FIG. 3.

The present invention is useful with digital records in the form of laser-readable codings on disks 10 which may be reproduced by record players 12. The controls for the record player typically include a manually adjustable volume controls 14 and a "play" button 16 which are to be manually actuated to initiate playback operation. These controls are often incorporated in a remote controlled handset (not shown) which communicates with the player 12 by infrared signals or the like. The sound output of the player may be reproduced over loudspeakers (not shown) but the advantages of the present invention are most critical when the listener uses earphones 18.

The present invention is equally applicable to digital signals encoded on other media such as tape or the like. The sound performance recorded on the media are typically music and a single record typically incorporates a number of musical selections which may be sequentially or randomly accessed. When the performances are reproduced sequentially, there is typically a time delay of 2-10 seconds between the playback of sequential performances.

One form of use of the invention simply consists of recording digital signals on the record media 10, preceding each musical performance. These record media may thus be used with a conventional, unaltered record player. FIG. 2 constitutes a plot of the intensity of the sounds reproduced from a digital record formed in accordance with the present invention illustrating periods of warning tones 20 followed by musical performances 22. In the interval between a pair of musical performances 20, the period in which the warning sound 20 is generated is preferably only a portion of the time interval between playback of the two performances, so that silence is generated for a period indicated at 24.

The warning sounds, which may be tones or music, continuous or interrupted, preferably have a maximum value substantially lower than the maximum amplitude of the sounds reproduced during the performance of the sections 20. Preferably, the maximum amplitude of the warning signal is about 10-30 db lower than the maximum amplitude of the performance. Accordingly, even if the volume control is set too high for comfort, the listener will not be disturbed by the warning sound, but will be alerted to adjust the volume control level before the playback of the recorded performance 20 occurs.

The record player schematically illustrated in FIG. 3 represents an alternative form of the invention which may be used with conventional digital records without special warning sound recordings and yet will produce the warning sound before the record player begins to reproduce the performance. The record player, generally indicated at 26, includes a pickup section 28 which may be an optical, using a laser, or other form. The output of the pickup 28 is provided to a two position switch 30. The other input to the switch comes from a digital signal source 32 within the player. This may constitute a read-only memory, constant member generator, or the like.

The output of the switch 30 is provided to a digital to analog converter 34 which in turn feeds an amplifier 36. The output of the amplifier, controlled by a volume control 38, is provided to the sound reproduction apparatus such as headphones or speakers 40.

The position of the switch 30 is controlled by a time delay generator 42. The manually actuated "play" button 16 which is actuated when the operator desires the performance to begin provides its output to the time delay circuit 42 which controls the switch 30 to provide signals from the warning tone generator 32 to the digital analog converter 34 and the amplifier 36. This results in generation of the warning sound plotted at 46 in FIG. 4. After the time delay, which may typically be 2 to 10 seconds in length, has terminated, the switch 30 turns to the pickup 28 and the performance recorded on the record media used with the system is reproduced, as indicated at 48 in FIG. 4. This embodiment may also include a manually actuated disable switch 44 which when actuated by the user disables the warning signal.

With this embodiment of the invention, the warning sound is generated even if the play of the record is initiated in the middle of a performance. If several performances are performed sequentially, without interruption, no warning sound is generated between the performances, but the warning sound generated at the initiation of the playback will suffice to allow proper adjustment of the volume control by the operator.