WO2008006376A1 - A method, apparatus, and system for spatial redistribution of direct and ambient sound. - Google Patents

Abstract

In spatial sound techniques involving direct sounds coming from front loudspeakers and ambient sounds that come from rear loudspeakers a balance control is used for left/right change and a fader control for front/rear change. The net result of the use of a simple fader will only constitute changes in the total amount of direct signal or the total amount of ambience. A fader according to the invention will provide a mix of both direct signal and ambience signal to both front and back loudspeakers such that the impression becomes one of moving inside a sound stage.

Description

A method, apparatus, and system for spatial redistribution of direct and ambient sound.

Technical field

The present invention relates generally to methods, devices, and systems for moving the apparent listening position within a listening space activated by individual sound sources providing sources of direct sounds predominantly from the front via loudspeakers and containing ambience information related to the arrival times and relative intensities of correlated signals, said ambience information arriving predominantly from the rear via loudspeakers, said device comprising a fader function and a balance function to act on a multi-channel signal. Such methods, devices, and systems may be used in modern home/domestic systems. More specifically such methods, devices, and systems may be used in automotive audio reproduction systems. This refers to the provision of audio in the cabin of cars.

Background of the invention

Almost all current automotive audio reproduction systems permit the user to make adjustments both to the timbral characteristics and the spatial representation of the audio signal being played. In home entertainment systems such functions are needed in conjunction with e.g. surround sound. The timbral characteristics are adjusted by means of a tone control. The spatial characteristics are typically controlled using two functions labelled:

1. Balance 2. Fader

The former of these permits the user to adjust the apparent location of the sound stage laterally in the car environment or a home cinema environment, as the case may be. That is to say that the image can be moved left and right of the listener. The fader controller traditionally has allowed the user to control the relative levels of the signals produced by the "front" and "back" loudspeaker channels, giving the ability to move the sound stage forwards and backwards in the listening space.

Typically, it is the objective of the ambient channels (usually allocated to the back loudspeakers in an automotive system) to provide a sensation of envelopment for the listener, whereas the front channels are typically used to present individual sources that are easily locatable in space.

In such a presentation with a spatial distribution where the direct sources are located forward of the listener and the ambience and reverberation to the rear of the listener, a simple, traditional Fader function will be detrimental to the overall audio quality. For example, moving the fader to the rear will result in an overabundance of reverberation and too little direct sound. Moving the fader to the front will result in a loss of envelopment and audible information about the recorded space.

In older systems, it was adequate to use the fader controller to simply adjust the relative levels of the various output channels of the audio reproduction system. Such systems are described in e.g.US Patents 3,784,748 and 5,073,944. However, as automotive audio systems have advanced with more loudspeakers, and more sophisticated 2-to-n channel upmixing algorithms, as well as the requirement for multichannel compatibility, this method is no longer adequate.

Summary of the invention

On the above background, it is the object of the present invention to provide a method and corresponding devices and systems that improve upon traditional methods, allowing for compatibility with current, more sophisticated systems.

A system that avoids the disadvantages of prior fader functions is particular in that the fader function acts on both the direct sound and the ambient sound represented by the multichannel signal in order that at one extreme setting, the distribution of direct sound and ambient sound is front and rear, respectively, while at the other extreme the distribution is the opposite, and in that a mixture of direct sound and ambient sound is provided at intermediate settings.

The system assumes that the signal being processed is multichannel (containing more than 2 audio channels) in nature. If the original signal is monophonic (one-channel) or stereophonic (two-channel) then some type of upmixing algorithm is necessary to separate the so-called "dry" or direct signals from the ambient components in the signal. These ambient components may be extracted from the original audio material or synthesised, or both, depending on the upmixing algorithm. However, the present invention requires that the audio signal be previously divided into front and rear stages that are intended to be presented to the listener in what is perceived as different spatial locations in the car or other listening space.

In order to alleviate the problems with simple systems, the proposed invention "swaps" the front and rear sound stages by means of backwards and forwards movements of the Fader control. In a central position, the front and back channels perform their duties as expected. That is to say, the front loudspeakers provide the front audio channels to the listener and the back loudspeakers produce the surround audio channels. As the Fader is moved to the front, the apparent level of the rear loudspeakers is reduced, and more of the surround (back) audio channels are distributed to the front loudspeakers, mixed with the front audio channels. If the Fader is turned to the back, then the system gradually redistributes the signals such that the front audio channels are sent to the back loudspeakers and the surround information is increased in the front loudspeakers.

An advantageous embodiment is particular in that in the intermediate settings, predetermined scaling factors are applied to the channels derived from the multichannel signal prior to summing for the individual loudspeakers. This permits a "tuning" of the degree of mixing of direct with ambient information.

One particular method of combining the signals is particular in that the direct-to- ambient energy ratio at the listening position is maintained independently of the fader function setting. An analogue means for obtaining a simple functionality is particular in that it comprises a four-gang potentiometer for each of the right and left channels, in which the wipers pick off fractional full-scale signals in such a way that the gain functions of two of the potentiometers are reversed, and that two fractional signals are summed differently for each of the front and rear loudspeakers in each of the right and left channels. This intuitively illustrates the principle behind the novel fader.

The end result is that the total envelopment or direct-to-reverberant sound ratio at the listening position is not changed, however, the listener's perception is that the sound sources are moved from front to back with an appropriate corresponding move of the fader controller.

Brief description of the figures

Fig. 1 shows an embodiment of the invention using analogue electronics,

Fig. 2 shows a digital signal-processing embodiment of the invention,

Fig. 3 shows an alternative digital signal-processing embodiment,

Fig. 4 shows a graph of the resulting levels to the loudspeakers from a signal processing as shown in Fig. 3, and

Fig. 5 shows a similar graph as the result of a different signal processing.

Fig. 1 shows a simple analogue circuit schematic representation of a possible embodiment of the system. It consists of two input channels, one intended for the front and the second for the back. These two signals are routed to two output channels, one for a front loudspeaker and the second for a back loudspeaker though four ganged potentiometers attached to a single user-controlled Fader control knob. The expression "ganged" refers to the fact that the potentiometer "wipers" are moved in synchronism, irrespective of the ohmic value of the potentiometers and controllable by any means, such as a common shaft, a chain drive, a gear wheel drive, or even when constructed as synchronously electronically controlled potentiometers, such as MOSFET combinations.

When the fader is turned entirely to the front, the front output is routed to the front loudspeaker and the back output is routed to the back loudspeaker. When the fader is turned entirely to the back, the front output is routed to the back loudspeaker and the back output is routed to the front loudspeaker. This figure shows the signal processing for only one side, either Left or Right, of a stereo audio signal.

Fig. 2 shows a digital signal processing schematic representation of a digital embodiment of the system. It consists of four input channels, two intended for the front and two for the back. These four signals are routed through the system to four output channels, two for a stereo pair of front loudspeakers and two for a stereo pair of back loudspeakers. A gain is applied to each signal according to the user's setting of the fader controller (the level adjustment means). When the fader is turned entirely to the front, the front inputs are routed to the front loudspeakers and the back inputs routed to the back loudspeakers. When the fader is turned entirely to the back, the front inputs are routed to the back loudspeakers and the back inputs routed to the front loudspeakers. In addition, for specific tuning purposes, a gain may be applied at any point in the signal flow to ensure that the appropriate amount of signal is delivered to the appropriate output.

Fig. 3 shows the programming of a digital signal processing system in order to obtain a level distribution in dependence of the Fader setting according to Fig. 4.

Fig. 4 schematically shows the relative levels (voltage or sound pressure, according to the method of measurement) of the contributions from the front and back output channels to the front and back loudspeakers in dependence of the fader setting at any position between "Back" and "Front". These graphs apply to the Left channel with the Left loudspeakers and the Right channel with the right loudspeakers. Fig. 5 shows a different distribution of the levels from that of Fig. 4, and it is obtained by using a different set of delimiters and functions in the general block schematic of Fig. 3.

The invention has been described in some detail above, but this is not limiting per se, as the skilled person will be able to devise additional mechanical, electronic, or digital solutions that perform in an equivalent manner, thereby obtaining similar advantageous results. In particular, a general purpose computer or a RISC processor may be programmed with such steps as to enable the device to perform in an equivalent manner to the embodiments described herein.

The foregoing description of the specific embodiments will so fully reveal the general nature of the present invention that others skilled in the art can, by applying current knowledge, readily modify or adapt for various applications such specific embodiments without undue experimentation and without departing from the generic concept, and therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. The means, materials, and steps for carrying out various disclosed functions may take a variety of forms without departing from the invention.

Thus, the expressions "means to ... " and "means for ...", or any method step language, as may be found in the specification above and/or in the claims below, followed by a functional statement, are intended to define and cover whatever structural, physical, or electrical element or structure, or whatever method step, which may now or in the future exist which carries out the recited functions, whether or not precisely equivalent to the embodiment or embodiments disclosed in the specification above, i.e., other means or steps for carrying out the same function can be used; and it is intended that such expressions be given their broadest interpretation.

Claims

1. A device for moving the apparent listening position -within a listening space activated by individual sound sources providing sources of direct sounds predominantly from the front via loudspeakers and containing ambience information related to the arrival times and relative intensities of correlated signals, said ambience information arriving predominantly from the rear via loudspeakers, said device comprising fader function means and balance function means to act on a multi-channel signal, characterised in that the fader function means act on both the direct sound and the ambient sound represented by the multi-channel signal in order that at one extreme setting, the distribution of direct sound and ambient sound is front and rear, respectively, while at the other extreme the distribution is the opposite, and in that a mixture of direct sound and ambient sound is provided at intermediate settings.

2. A device according to claim 1, characterised in that in the intermediate settings, predetermined scaling factors are applied by level adjustment means to the channels derived from the multi-channel signal prior to summing for the individual loudspeakers.

3. A device according to claim Ior2, characterised in that the direct-to- ambient energy ratio at the listening position is controlled throughout all settings of the fader function means by means of controllable level adjustment means.

4. A device according to claim 3, characterised in that the direct-to- ambient energy ratio at the listening position is maintained at all settings of the fader function means.

5. A device according to claim 1, characterised in that it comprises a four-gang potentiometer for each of the right and left channels, in which the wipers pick off fractional full-scale signals in such a way that the gain functions of two of the potentiometers are reversed, and that two fractional signals are summed differently for each of the front and rear loudspeakers in each of the right and left channels.