Volume control for audio signals
A motion picture soundtrack reproduction system has a center front soundtrack channel and a plurality of other soundtrack channels. A volume control adjusts the gain of all the channels. The volume control has a range of settings from a minimum to a maximum, the gain of the center front channel having substantially a first relationship to the volume control settings and the gain of the other channels having substantially a second relationship to the volume control settings, the relationships being such that for a range of volume control settings less than a first setting the gain of the center front channel remains substantially constant while the gain of the other channels decreases as the setting decreases or decreases more gradually than the gain of the other channels as the setting decreases.
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More than one Reissue Application has been filed for the reissue of U.S. Pat. No. 7,251,337, issued Jul. 31, 2007. The reissue applications are application Ser. Nos. 12/493,111 filed Jun. 26, 2009, 13/341,871 filed Dec. 30, 2011, 13/341,861 filed Dec. 30, 2011, now reissue Pat. No. RE44,261, issued Jun. 4, 2013, 13/341,873 filed Dec. 30, 2011, now reissue Pat. No. RE44,929, issued Jun. 3, 2014, and 13/341,870 filed Dec. 30, 2011. The present application claims the benefit as a Reissue Continuation Application of application Ser. No. 12/493,111, filed Jun. 26, 2009 (now RE43,132, issued on Jan. 24, 2012), which is a Reissue Application of U.S. Pat. No. 7,251,337, issued Jul. 31, 2007 (application Ser. No. 10/423,829, filed Apr. 24, 2003), the entire contents of all of the foregoing are hereby incorporated by reference as if fully set forth herein, under 35 U.S.C. §120. Applicants hereby rescind any disclaimer of claim scope in the parent application(s) or the prosecution history thereof and advise the USPTO that the claims in this application may be broader than any claim in the parent application(s).
TECHNICAL FIELDThe invention relates generally to the processing of audio signals. More particularly, the invention relates to control of the loudness of motion picture soundtracks when reproduced.
BACKGROUND ARTIn the mid-1970s, Dolby Laboratories introduced a calibration recommendation for monitor levels in movie soundtracks (“Dolby” is a trademark of Dolby Laboratories, Inc.). A pink noise reference signal was used in the record chain to adjust the audio monitor level to 85 dBc. All theatres equipped for playback of the new stereo optical soundtracks were set up such that an equivalent pink noise signal in a soundtrack channel generated the same 85 dBc with the playback volume control (fader) set to the calibrated setting. This meant that theatres playing films at the calibrated volume control setting (a setting of “7” in a range of “0” to “10” on most cinema processors) reproduced the same loudness level selected by the film director and audio engineers in the dubbing theatre (referred to herein as “the mixer”).
This system worked quite well for many years. Dolby Stereo (A-type encoded) films had limited headroom and the resulting constrained dynamic range yielded few audience complaints. Most theatres played films at the calibrated level. Soundtrack format technology has been significantly enhanced since Dolby Stereo. Dolby SR extended the head-room by 3 dB at midrange frequencies, and more at low and high frequencies. In recent years, the new digital formats have further increased the headroom.
Because the 85 dBc calibration technique has been maintained throughout evolving format changes, additional headroom is available on the newer soundtracks. However, feature films do have a consistent, subjective mix reference, independent of increased headroom, for dialogue record level, known as “associative loudness.” When the dubbing mixer sees an actor on the screen, and there is no conflict between the dialogue and music or effects, the dialogue level in a moderate close-up is set to be plausible for the visual impression. Within reasonable limits, this generally holds true to within 2 or 3 dB. This natural dialogue level does not hold true for narration, as there is no corresponding visual reference. Music and effects have no direct visual associative loudness. Most people are not familiar with the actual sound pressure levels of a Concorde takeoff or a 50 mm howitzer. The music score level is equally uncalibrated.
As the headroom capability of the recording medium has been extended, it has certainly been used: the “non-associative” loudness of effects and music has risen to fill the available headroom space. Using dialogue as a reference, loud sounds like explosions are often 20 dB or more louder (explosions reach full scale peak level of 25 dB above dialogue level), and some quiet sounds, which are intended to be heard by all listeners, such as leaves rustling, may be 50 dB quieter.
In response to audience complaints that movies are too loud, many theatres are playing films substantially below the calibrated level. A volume control setting (fader level) of “6” or “5½,” as opposed to the calibrated level (volume control standard setting) of “7,” is not uncommon, representing a loudness reduction of approximately 4 or 6 dB. Some cinemas have their volume control permanently turned down to such settings because projectionists operating multiplexes with many screens showing different movies simultaneously don't have the time or cannot be bothered to set the controls differently for different movies. If the volume control is turned down to avoid complaints of excessive loudness, the dialogue is quieter than the mixer intended, and audiences may complain instead that some dialogue is not intelligible in the presence of other sounds in the film and/or general background noise of the theater (popcorn eating, air-conditioning, people talking, etc.). Theatre playback levels are often set by complaints generated by the loudest (and earliest) element of the show. If the playback level is set in response to the loudest trailer (preview), which is often louder than the feature film, the feature often plays at the same reduced level. The result is that the dialogue level of the feature is lowered by the same level deemed necessary to attenuate the trailer. A feature film played with a loudness 6 dB below the calibrated level may have serious dialogue intelligibility problems and very quiet sounds may become inaudible.
In addition, it is possible that the increased use of head-room from Dolby A-type to Dolby SR and digital releases has not been matched by a corresponding increase in power amplifier and loudspeaker capability. The resultant distortion from overloaded equipment may well exacerbate the loudness problems of recent soundtracks, causing increased incidence of complaints.
In early cinema sound equipment employing calibration, the volume control was a mechanical potentiometer, often with a click-stop or detent at the standard setting. More recent (digital) equipment uses a shaft encoder or a pair of up-down buttons (with a numeric display for the setting), delivering a control signal that operates on multipliers (either digital or voltage-controlled amplifiers) to affect the gain applied to all channels of the reproduced soundtracks. In typical cinema sound equipment, the volume control varies the gain gradually and relatively uniformly over a range of settings from about “4” to “10,” with the gain falling more rapidly at setting below about “4,” allowing a fade to inaudibility. Such a typical prior art relationship between gain or loss and volume control setting is shown in the lower curve of
With the exception of monophonic installations, to which the present invention does not apply, all movie sound installations include three or more front loudspeakers including a center front. Historically, film mixers place dialogue in the center front channel and it is rare for speech from an on-screen actor to be placed anywhere else. This applies both for a multitrack digital soundtrack (for instance 5.1- or 7.1-channels) or a two-channel analog optical soundtrack reproduced via a matrix decoder to derive left, center, right and surround outputs. The center front channel may of course contain other material, but, generally, it is material important in following the action of the movie because the audience's attention is focused on the screen. At moments when the soundtrack is loud enough to provoke complaint, several channels are generally contributing to that loudness, not just any one, and in particular not just the center front.
DISCLOSURE OF INVENTIONIn accordance with the present invention, a motion picture soundtrack reproduction system comprises a center front soundtrack channel and a plurality of other soundtrack channels. A volume control adjusts the gain of all the channels, the volume control having a range of settings from a minimum to a maximum, the gain of the center front channel having substantially a first relationship to the volume control settings and the gain of the other channels having substantially a second relationship to the volume control settings, the relationships being such that for a range of volume control settings less than a first setting the gain of the center front channel remains substantially constant while the gain of the other channels decreases as the setting decreases or decreases more gradually than the gain of the other channels as the setting decreases.
Also in accordance with the present invention, a motion picture soundtrack reproduction system comprises a center front soundtrack channel and a plurality of other soundtrack channels, each of the channels having adjustable gain and one or more loudspeakers, and a controller having a volume control for adjusting the gain of all the channels, the volume control having a range of settings from a minimum to a maximum, the gain of the center front channel having a first relationship to the volume control settings and the gain of the other channels having a second relationship to the volume control settings, the relationships being such that for a range of volume control settings less than a first setting the gain of the center front channel remains substantially constant while the gain of the other channels decreases as the setting decreases or decreases more gradually than the gain of the other channels as the setting decreases.
The range of volume control settings less than the first setting extends down to the minimum control setting or, alternatively, down to a second setting above the minimum control setting. In the latter case, for settings less than the second setting the gains of all the channels decrease in substantially the same way as the setting decreases and for such volume control settings the gain of the center front channel is greater than the gain of the other channels. Optionally, for settings less than the second setting the gain of the center front channel is greater than the gain of the other channels by a substantially constant amount in the logarithmic domain.
For settings greater than the first setting the gains of all the channels may increase as the setting increases and for each of such volume control settings the gain of the center front channel and the gain of the other channels may be substantially the same.
The invention is particularly advantageous in an arrangement in which when the volume control is set to a standard setting, each of the channels has a respective gain that produces a respective standard acoustic level in response to a signal having a respective standard reference level in the channel. In that case, the first setting is about the standard setting.
The invention provides for reducing the maximum loudness, and thereby avoiding complaints, while maintaining the acoustic level of the center front containing dialogue and requiring only one user-operated control. According to an embodiment of the invention, the cinema equipment is designed and installed in the conventional manner to the extent that with the volume control nominally at its standard setting, each of the reproduced soundtrack channels has a respective gain that produces a respective standard acoustic level in response to a signal having a respective standard reference level in the channel, thus matching the standard levels in a film mixing room. Thus, when calibrated, the playback system with its volume control at the standard setting has an apparent loudness that is substantially the same as that intended by the film mixer. However, in accordance with the present invention, if the volume control is turned down below the standard setting in response to actual (or expected) complaints from the audience, over a limited range of settings all channels except the center front are attenuated equally, but the center front is reduced by a smaller degree (or not at all). The effect is not only a reduction in the overall loudness but an increase in the proportionate contribution of the center front channel, with a potential improvement in intelligibility when the other channels are loud. Optionally, after some degree of changing the balance of the center front to other channels down to a setting below the standard setting, for further lowering of the settings all channels are attenuated equally, maintaining fixed the altered balance.
Still referring to
An exemplary system according to the present invention is shown in
In a practical arrangement employing digital controls, as shown in
The present invention and its various aspects may be implemented in analog circuitry, for example, with two suitable non-linear functions relating control setting to gain, or as software functions performed in digital signal processors, programmed general-purpose digital computers, and/or special purpose digital computers, or some combination of such devices and functions. Interfaces between analog and digital signal streams may be performed in appropriate hardware and/or as functions in software and/or firmware.
Claims
1. A motion picture soundtrack reproduction system, the system having a center front soundtrack channel and a plurality of other soundtrack channels, comprising
- a controller having a volume control for adjusting the gain of all the channels, the volume control having a range of settings from a minimum to a maximum, the controller having a first output for controlling the gain of the center front channel and a second output for controlling the gain of the other channels in response to settings of the volume control, the gain of the center front channel having a first relationship to the volume control settings and the gain of the other channels having a second relationship to the volume control settings, the relationships being such that for a range of volume control settings less than a first setting the gain of the center front channel (1) remains substantially constant while the gain of the other channels decreases as the setting decreases, or (2) decreases snore gradually than the gain of the other channels as the setting decreases.
2. A motion picture soundtrack reproduction system, comprising
- a center front soundtrack channel and a plurality of other soundtrack channels, each of said channels having adjustable gain and one or more loudspeakers, and
- a controller having a volume control for adjusting the gain of all the channels, the volume control having a range of settings from a minimum to a maximum, the controller having a first output for controlling the gain of the center front channel and a second output for controlling the gain of the other channels in response to settings of the volume control the gain of the center front channel having a first relationship to the volume control settings and the gain of the other channels having a second relationship to the volume control settings, the relationships being such that for a range of volume control settings less than a first setting the gain of the center front channel (1) remains substantially constant while the gain of the other channels decreases as the setting decreases or (2) decreases more gradually than the gain of the other channels as the setting decreases.
3. A system according to claim 1 or claim 2 wherein the range of volume control settings less than said first setting extends down to the minimum control setting.
4. A system according to claim 1 or claim 2 wherein the range of volume control settings less than said first setting extends down to a second setting above the minimum control setting.
5. A system according to claim 3 wherein for settings less than said second setting the gains of all the channels decrease in substantially the same way as the setting decreases and for such volume control settings the gain of the center front channel is greater than the gain of the other channels.
6. A system according to claim 5 wherein for settings less than said second setting the gain of the center front channel is greater than the gain of the other channels by a substantially constant amount in the logarithmic domain.
7. A system according to claims 1 wherein for settings greater than said first setting the gains of all the channels increase as the setting increases and for each of such volume control settings the gain of the center front channel and the gain of the other channels are substantially the same.
8. A system according to claims 1 wherein when the volume control is set to a standard setting, each of the channels has a respective gain that produces a respective standard acoustic level in response to a signal having a respective standard reference level in the channel.
9. A system according to claim 8 wherein said first setting is about said standard setting.
10. A method for volume control of audio signals, comprising:
- reducing a setting of a volume control in response to a first element of an audio signal, the setting ranging from a minimum to a maximum;
- in response to the reducing, adjusting a gain of a first channel of a second element of the audio signal and a gain of a second channel of the second element of the audio signal, for a range of volume control settings less than a first setting the adjusting both decreases loudness and increases a contribution of the first channel to the loudness of a reproduced second element of the audio signal, for a range of volume control settings less than a second setting the adjusting decreases the gain of the first channel in a substantially same manner as the gain of the second channel is decreased as the setting of the volume control is reduced;
- feeding an audio signal of the first channel to a first output;
- feeding an audio signal of the second channel to a second output;
- wherein the first element of the audio signal and the second element of the audio signal are different elements within the audio signal.
11. The method of claim 10, wherein the reducing employs digital controls.
12. The method of claim 10, wherein the second output is at least one of a left output, right output, and surround output.
13. The method of claim 10, wherein first output is a center channel output.
14. The method of claim 10, wherein the first element of the audio signal is a trailer and the second element of the audio signal is a feature film.
15. The method of claim 10, wherein the first element of the audio signal and the second element of the audio signal are in a Dolby Digital format.
16. The method of claim 10, wherein the first element of the audio signal and the second element of the audio signal are digital streams.
17. The method of claim 10, wherein the first element of the audio signal and the element of the audio signal are multitrack digital soundtracks.
18. An apparatus for volume control of audio signals, comprising:
- a subsystem, implemented at least partially in hardware that reduces a setting of a volume control in response to a first element of an audio signal, the setting ranging from a minimum to a maximum;
- a subsystem, implemented at least partially in hardware that, in response to the reducing, adjusts a gain of a first channel of a second element of the audio signal and a gain of a second channel of the second element of the audio signal, for a range of volume control settings less than a first setting the adjusting both decreases loudness and increases a contribution of the first channel to the loudness of a reproduced second element of the audio signal, for a range of volume control settings less than a second setting the adjusting decreases the gain of the first channel in a substantially same manner as the gain of the second channel is decreased as the setting of the volume control is reduced;
- a subsystem, implemented at least partially in hardware that feeds an audio signal of the first channel to a first output;
- a subsystem, implemented at least partially in hardware that feeds an audio signal of the second channel to a second output;
- wherein the first element of the audio signal and the second element of the audio signal are different elements within the audio signal.
19. The apparatus of claim 18, wherein the reducing subsystem employs digital controls.
20. The apparatus of claim 18, wherein the second output is at least one of a left output, right output, and surround output.
21. The apparatus of claim 18, wherein first output is a center channel output.
22. The apparatus of claim 18, wherein the first element of the audio signal is a trailer and the second element of the audio signal is a feature film.
23. The apparatus of claim 18, wherein the first element of the audio signal and the second element of the audio signal are in a Dolby Digital format.
24. The apparatus of claim 18, wherein the first element of the audio signal and the second element of the audio signal are digital streams.
25. The apparatus of claim 18, wherein the first element of the audio signal and the second element of the audio signal are multitrack digital soundtracks.
26. A non-transitory computer readable medium, storing software instructions for volume control of audio signals, which when executed by one or more processors cause performance of the steps of:
- reducing a setting of a volume control in response to a first element of an audio signal, the setting ranging from a minimum to a maximum,
- in response to the reducing, adjusting a gain of a first channel of a second element of the audio signal and a gain of a second channel of the second element of the audio signal, for a range of volume control settings less than a first setting the adjusting both decreases loudness and increases a contribution of the first channel to the loudness of a reproduced second element of the audio signal, for a range of volume control settings less than a second setting the adjusting decreases the gain of the first channel in a substantially same manner as the gain of the second channel is decreased as the setting of the volume control is reduced;
- feeding an audio signal of the first channel to a first output;
- feeding an audio signal of the second channel to a second output;
- wherein the first element of the audio signal and the second element of the audio signal are different elements within the audio signal.
27. The non-transitory computer readable medium of claim 26, wherein the reducing employs digital controls.
28. The non-transitory computer readable medium of claim 26, wherein the second output is at least one of a left output, right output, and surround output.
29. The non-transitory computer readable medium of claim 26, wherein first output is a center channel output.
30. The non-transitory computer readable medium of claim 26, wherein the first element of the audio signal is a trailer and the second element of the audio signal is a feature film.
31. The non-transitory computer readable medium of claim 26, wherein the first element of the audio signal and the second element of the audio signal are in a Dolby Digital format.
32. The non-transitory computer readable medium of claim 26, wherein the first element of the audio signal and the second element of the audio signal are digital streams.
33. The non-transitory computer readable medium of claim 26, wherein the first element of the audio signal and the second element of the audio signal are multitrack digital soundtracks.
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Type: Grant
Filed: Dec 30, 2011
Date of Patent: Feb 24, 2015
Assignee: Dolby Laboratories Licensing Corporation (San Francisco, CA)
Inventor: Stephen M. Jacobs (Cupertino, CA)
Primary Examiner: Disler Paul
Application Number: 13/341,870
International Classification: H03G 3/00 (20060101);