EP0714222A2 - Pseudostereo processor for mobile receiver - Google Patents

Abstract

When a single-channel audio signal is present it is converted into a pseudo-stereo signal and distributed to two loudspeakers by a multiplexing unit. The quality of reception is evaluated by another circuit so that when it falls below a limit of acceptability the system is switched from stereo to mono operation in good time. The multiplex output from the FM tuner is applied to a stereo decoder which addresses a control unit causing the multiplexer to switch the loudspeaker inputs correctly according to the available signal in less than 100 ms.

Description

The invention relates to a mobile radio receiver according to the preamble of claim 1. Such mobile radio devices are known in a variety of designs. As far as stereo receivers are concerned, they show a switch from stereo mode to mono mode if the reception quality decreases. Mono operation does not sufficiently satisfy the listener's sense of sound. Almost every mobile radio receiver has the option of manually adjusting the sound parameters such as height, bass, balance or fader in mono operation, but these variation options do not create the possibility of a sufficient sound experience comparable to that of stereo reception, especially since these settings unsatisfactorily make the driver of a radio listening Way distracts from traffic.

Various methods for generating pseudo stereo signals are also known, cf. Philips Journal of Research Vol. 39 No.3 1984 pp. 94ff. However, due to the extensive computing power required and the associated circuitry involved, these methods can only be implemented in stationary and large-volume devices.

Taking this prior art into account, the invention is based on the object of creating a mobile radio receiver which offers the user a sound experience close to that of stereo reception even under difficult reception conditions without complex operation.

To solve this problem in a mobile radio receiver of the type mentioned, it is proposed to provide it with a pseudo-stereo circuit, which ensures that automatically when a mono signal is present, it is converted into a pseudo-stereo signal and thereby a user particularly pleasant feeling of sound is conveyed. The pseudo-stereo circuit is always active as soon as the mobile radio receiver is not able to receive a stereo signal of sufficient quality due to the broadcast radio signal or due to the current local reception conditions, which leads to an automatic switchover from stereo to Mono reception of the radio receiver leads. In both cases, the unpleasant sound experience of the flat mono signal is automatically upgraded to a pleasant spatial and full sound experience due to the pseudo-stereo sound, i.e. without complex adjustments, which are associated with a dangerous reduction in the driver's attention to traffic.

This upgrading allows the driver to experience a largely uniform and pleasant sound experience, which affects his attention much less than the unpleasant dynamic switching between the pleasant stereo operation and the already unpleasant mono operation.

It has proven to be particularly advantageous to continue to maintain the pleasant sound experience by increasing the limit value of the reception quality for switching from stereo to mono operation, with increased reception power due to the increased band gap. By increasing the limit, the radio receiver is already switched to mono operation if the stereo reception situation is still possible, which automatically leads to a pseudo stereo signal without the driver having to influence the driver to use the pseudo stereo circuit and thus to process the mono signal. The limit value is chosen so that reception that is always interference-free, in particular overlay-free, is reliably possible. It is possible to select the limit value in each case adapted to the area of application of the mobile radio receiver.

A switchover unit is preferably provided which, controlled by the quality of the received signal, switches in a defined manner between the stereo signal and the pseudo-stereo signal which was formed by the pseudo-stereo circuit from the received mono signal.

According to a further feature of the invention, it is proposed to carry out the switching process in a period of less than 100 ms, which means that the pure switching process cannot be perceived by the relatively sluggish human ear, since there are regularly gaps in reception of a length below not perceive this period of time. This design according to the invention makes it possible to disguise the pure switching process and thus almost to hide the listener.

An alternative embodiment of the invention shows the switching process in the form of a cross-fade, which is completed within a period of the order of a second. The cross-fading takes place continuously and not abruptly, which gives the listener the opportunity to get used to the changed sound conditions and thus achieve a pleasant switch from one sound state to the other. In particular, it is possible to get the listener used to the final state, which has changed compared to the initial state, and although there are only slight differences despite sophisticated pseudo-stereo circuits, it is nevertheless present. This soft crossfading thus represents an optimized and very pleasant form of switching for the listener.

An advantageous embodiment of the invention results from the combination of the two different switching principles in that the transition from stereo to pseudo-stereo reception uses cross-fading and the transition from pseudo-stereo to stereo reception takes place in less than 100 ms . With this special form it is possible to slowly get the listener used to the poorer pseudo-stereo experience, which results in the usual unobtrusive and therefore very pleasant transition to the poorer sound image. On the other hand, the fast, hard type of switching from poorer to better stereo reception is specifically chosen, since here the advantage of stereo reception comes into its own with a sufficiently advantageous sound experience during switching. This combination thus enables the apparently reluctant switching principles to be combined to form a particularly advantageous overall device, which enables the radio receiver to be switched from stereo to pseudo-stereo reception in a sound-optimized manner.

The changeover process is preferably carried out according to a predetermined changeover characteristic. The switchover characteristic is selected so that the listener perceives a switch from one to the other state as pleasantly as possible. Examples of suitable characteristic curve forms are, without being restricted to these, linear courses or such third degree.

A circuit for recognizing speech shows a special design of the radio receiver according to the invention. This detects speech components in the received or demodulated signal and controls the pseudo-stereo circuit in the presence of speech in such a way that the processing of the mono signal into a pseudo-stereo signal is prevented. This training makes it possible to make speech signals particularly clear to the listener. Surprisingly, processing the mono signal into a pseudo-stereo signal is not advantageous for speech, because the intelligibility of the speech signal suffers, which is of central importance. Behind it must be the feeling of sound. Through this training, the user succeeds in important information, such as e.g. To receive traffic announcements or alarm messages in a particularly understandable form without at the same time foregoing the special sound sensation in music or the like.

In one embodiment of the invention, the radio signal, either the received or the demodulated signal, is statistically evaluated for the temporal and frequency characteristics in the circuit for recognizing speech. Based on the evaluation, a reliable statement can be made as to whether the signal is speech or other signals. In an alternative embodiment, the RDS signal is evaluated by an RDS decoder for the PTY signal (Program Type Signal). If the evaluation shows that the PTY signal is a speech signal, the pseudo stereo circuit is deactivated. A corresponding arrangement results when a traffic announcement - a voice signal - is recognized by a traffic announcement decoder, which is known in large numbers, and the pseudo-stereo circuit is likewise deactivated by this. These different variants can be implemented independently of one another individually or together side by side. All combinations show the aforementioned advantageous effect.

According to a feature of the invention, the pseudo-stereo circuit is formed by two circuits, one for the left and one for the right channel. Both circuits are designed accordingly. One circuit contains a delay element to which on the one hand the input signal and on the other hand the delayed signal amplified and fed back by a factor g is supplied. The signal delayed in the delay element by the time del is subsequently amplified again by the factor -g before it is fed to the output for this channel in conjunction with the input signal. The structure of the other circuit for the other channel corresponds to that of the former, whereby it should be noted that the factor -g and vice versa is set instead of the gain factor g. This simple type of pseudo-stereo circuit makes it possible to generate a spatial sense of sound close to the stereo signal in a relatively simple manner.

bzw $\text{g** = g - 1}$

verstärkten Monosignal verknüpft wird. Die verknüpften Signale bilden dann die Ausgangssignale für den linken bzw. rechten Kanal. Diese weiter vereinfachte Schaltung zeigt bei vergleichbarer räumlicher Auflösung aufgrund der erhöhten Verwendung gemeinsamer Bauteile für die beiden Schaltkreise einen geringeren Schaltungsaufwand, der sich in geringerer Anfälligkeit und geringeren Kosten widerspiegelt.In an alternative, further simplified embodiment of the pseudo stereo circuit, the mono signal is fed to a delay element, which delays it by the time del. This signal is then amplified in an amplifier stage by the amplification factor g, which is between 0 and 1. The delayed and amplified signal is then fed to the two separate circuits for the left and right channels, where it is by a factor in each mixer $\text{g * = 1 - g}$

respectively $\text{g ** = g - 1}$

amplified mono signal is linked. The linked signals then form the output signals for the left or right channel. This further simplified circuit shows, with comparable spatial resolution, due to the increased use of common components for the two circuits, less circuit complexity, which is reflected in less susceptibility and lower costs.

According to a further feature of the invention, the time del and / or the factors g are selected so that the user experiences an optimized surround sound in each specific vehicle.

The following exemplary embodiments of the invention reveal further advantageous features and special features which are described and explained in more detail below with reference to the illustration in the drawings.

Fig. 1

einen schematischen Aufbau des mobilen Rundfunkempfängers mit einer Pseudo-Stereo-Schaltung,

Fig. 2

eine Schaltungsanordnung für eine Pseudo-Stero-Schaltung,

Fig. 3

eine zweite Schaltungsanordnung für eine Pseudo-Stereo-Schaltung,

Fig. 1 zeigt einen Tuner, der hier als FM-Tuner ausgebildet ist, welcher das demodulierte Signal dem Stereodecoder zuführt, welcher mit der Control Unit verbunden ist und dieser das Vorliegen eines Stereo- bzw. eines Monosignals meldet. Das vom Stereodecoder abgegebene Signal wird einerseits einer Umschalteinheit zugeführt und andererseits einer Pseudo-Stereo-Schaltung zugeführt, die das zugeleitete Signal zu einem Pseudo-Stereosignal aufbereitet und im folgenden der Umschalteinheit zuführt. Die Umschalteinheit schaltet gesteuert durch die Control Unit zwischen den zugeführten Signalen hin und her. Erkennt der Stereodecoder also das Vorliegen eines Monosignals, wird die Control Unit darüber informiert, die dann automatisch das durch die Pseudo-Stereo-Schaltung zum Pseudo-Stereosignal aufbereitete Monosignal über die Umschalteinheit an die Lautsprecher für den linken und rechten Kanal weiterleitet. Diese Schaltung gewährleistet also ein völlig automatisches Umschalten zwischen Stereosignal und dem Pseudo-Stereosignal, welches durch die Pseudo-Stereo-Schaltung aus einem Monosignal gebildet wurde. Der Umschaltvorgang wird dabei nach in der Umschalteinheit fest abgespeicherten Umschaltkennlinien vorgenommen, wobei bevorzugt ein "hartes'' Umschalten mit einer Zeit von weniger als 100 ms von Pseudo-Stereo zu Stereo und ein "weiches" Umschalten in Form eines Umblenden über einen Zeitraum in der Größenordnung von einer Sekunde gewählt ist. Dabei ist es ohne Bedeutung, aus welchem Grund das Monosignal entstanden ist, d.h. es ist unabhängig davon, ob nur ein Monosignal empfangen wurde oder aufgrund der schlechten Empfangsbedingungen des Stereosignals dieses nur als Monosignal empfangen und verstärkt wurde.Show it

Fig. 1

1 shows a schematic structure of the mobile radio receiver with a pseudo stereo circuit,

Fig. 2

a circuit arrangement for a pseudo-stereo circuit,

Fig. 3

a second circuit arrangement for a pseudo stereo circuit,

Fig. 1 shows a tuner, which is designed here as an FM tuner, which feeds the demodulated signal to the stereo decoder, which is connected to the control unit and which reports the presence of a stereo or a mono signal. The signal emitted by the stereo decoder is supplied on the one hand to a switchover unit and on the other hand to a pseudo-stereo circuit which processes the supplied signal into a pseudo-stereo signal and subsequently feeds it to the switchover unit. The switchover unit switches between the supplied signals controlled by the control unit. If the stereo decoder detects the presence of a mono signal, the control unit is informed, which then automatically forwards the mono signal processed by the pseudo stereo circuit to the pseudo stereo signal via the switchover unit to the loudspeakers for the left and right channels. This circuit thus ensures a completely automatic switching between the stereo signal and the pseudo-stereo signal, which was formed by the pseudo-stereo circuit from a mono signal. The switching process is carried out according to the switching characteristics permanently stored in the switching unit, preferably a "hard" switching with a time of less than 100 ms from pseudo-stereo to stereo and a "soft" switching in the form of a switching over a period in the It is irrelevant for what reason the mono signal originated, ie it is irrelevant whether only a mono signal was received or because of the poor reception conditions of the stereo signal, it was only received and amplified as a mono signal.

2 and 3 show two alternatives for the basic structure of pseudo stereo circuits. 2, the mono signal is supplied. In the respective circuit for the left or right channel, this is combined with a signal delayed by a delay element by the time del and amplified by an amplifier stage by g or -g, which in turn is fed to the delay element. The delayed signal is subsequently amplified in a second amplifier stage by the factor -g or g, in turn linked to the mono signal and fed to the right or left output channel of the pseudo-stereo circuit.

bzw. $\text{g**=g-1}$

verstärkten Monosignal verknüpft wird und dem jeweiligen Ausgangskanal der Pseudo-Stereo-Schaltung zugeführt wird.3, the mono signal is delayed in a delay element common to both circuits by the time del and amplified in a common amplifier stage by the factor g, which is between 0 and 1. This delayed and amplified mono signal is then fed to the two circuits for the left and right channels, where it is in each case in a mixer stage with that of an amplifier stage arranged in each circuit by the factor $\text{g * = 1-g}$

respectively. $\text{g ** = g-1}$

amplified mono signal is linked and fed to the respective output channel of the pseudo stereo circuit.

Claims (14)

Mobile radio receiver characterized in that
a pseudo stereo circuit is provided which, in the presence of a mono signal, processes it into a pseudo stereo signal and feeds it to the loudspeakers, and that a quality evaluation circuit is provided, by means of which a switch from stereo operation to mono operation can be carried out if the reception quality drops below a limit value and in the following the preparation for the pseudo stereo signal can be triggered. Mobile radio receiver according to Claim 1, characterized in that the limit value is selected such that an early switchover to mono operation is possible even with sufficiently interference-free stereo reception. Mobile radio receiver according to one of the preceding claims, characterized in that a switchover unit is provided, by means of which a switchover between the stereo signal and the pseudo-stereo signal can be carried out by the pseudo-stereo circuit. Mobile radio receiver according to claim 3, characterized in that the switching unit is designed such that the switching process is completed in less than 100 ms. Mobile radio receiver according to claim 3, characterized in that the switching unit is designed such that the switching process in the form of a cross-fade is completed within a period of about 1s. Mobile radio receiver according to claim 4 and 5, characterized in that the switching unit is designed so that the switching process to pseudo-stereo in the form of a fade is completed within a period of about 1s and that the switching process from pseudo-stereo to stereo in less than 100 ms is completed. Mobile radio receiver according to one of the preceding claims, characterized in that a circuit for recognizing speech in the receiving or in the demodulated signal is provided, which is connected to the pseudo-stereo circuit and by means of which, in the presence of speech components, the mono signal is processed into pseudo -Stereo signal can be prevented. Mobile radio receiver according to one of the preceding claims, characterized in that the pseudo-stereo circuit for the two stereo channels L, R each have a separate circuit which contains a delay element (delay by del), the input of which is linked to the mono signal by the Factor g amplified and fed back output signal of the delay element is fed and its output signal is amplified by the factor -g and then combined again with the mono signal, the factor g being chosen positive for the stereo channel L and the factor g negative being chosen for the other stereo channel R. . Mobile radio receiver according to one of the preceding claims 1 to 7, characterized in that the pseudo-stereo circuit for the two stereo channels L, R each have a separate circuit in which a mixer is provided, which by a delay element by the time del delayed and by an amplifier stage by g $\text{(0 ≦ g ≦ 1)}$

amplified mono signal with the undelayed one channel around $\text{g * = 1-g}$

and for the other channel $\text{g ** = g-1}$

amplified mono signal and feeds it to the respective channel output. Mobile radio receiver according to claim 8 or 9, characterized in that the factor g is adjustable. Mobile radio receiver according to claims 8, 9 or 10, characterized in that the delay del is adjustable. Mobile radio receiver according to claim 7, characterized in that the circuit for recognizing speech contains an analysis circuit for the temporal or frequency course of the radio signal, which records the course, statistically evaluates it and supplies the result of the evaluation to the pseudo-stereo circuit. Mobile radio receiver according to Claim 7, characterized in that the circuit for recognizing speech is designed in such a way that it reads the PTY signal from the RDS signal and, when the "speech" signal is present, feeds it to the pseudo-stereo circuit. Mobile radio receiver according to Claim 7, characterized in that the circuit for recognizing speech contains a detector for the traffic announcement identification, which is connected to the pseudo-stereo circuit and which prevents processing when traffic announcements are present.

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