EP0714222B1 - 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 radios are known in a variety of designs. They show, as far as it is stereo receiving devices, with decreasing reception quality switching from stereo to mono mode. Mono operation does not adequately satisfy the listener's sense of sound. Although almost all mobile radio receivers have the ability to manually adjust the sound parameters such as treble, bass, balance or fader in mono mode, these variations do not create the possibility of a sufficient sound experience comparable to that of stereo reception, especially as these settings make the consciousness of a radio-listening driver unsatisfactory Distracting way from traffic.

Furthermore, various methods for generating pseudo-stereo signals are known, cf. Philips Journal of Research Vol. 39 No.3 1984 p. 94ff. , However, due to the required extensive computing power and the associated circuit complexity, these methods can only be implemented in stationary and large-volume devices. Radio receivers with a pseudo-stereo circuit are also off US-A-4833715 known.

The invention is taking into account this prior art, the object to provide a mobile radio receiver, which offers the user even under difficult reception conditions without complex operation, a sound experience near the stereo reception.

EP-A-0 503 154 discloses a mobile radio receiver with a pseudo stereo circuit which can be activated in music programs in mono. This is subject to binding in the RDS signal with sustained M / S coding (music / voice)

To solve this problem in a mobile radio receiver of the type mentioned is proposed to provide this with a pseudo-stereo circuit, which ensures that automatically in the presence of a mono signal, this is converted into a pseudo-stereo signal and thereby the user particularly pleasant sound perception is conveyed.

The radio receiver according to the invention shows a circuit for recognizing speech. This detects speech components in the received or demodulated signal and, in the presence of speech, controls the pseudo-stereo circuit 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. For speech processing of the mono signal to the pseudo-stereo signal is surprisingly not advantageous, because it suffers the clarity of the speech signal, which is of central importance. Behind it, the sense of sound has to stand back. With this design, the user, without any operation of the device, manages to obtain important information, e.g. To perceive traffic announcements or alarm messages in a particularly understandable form, without sacrificing the special sound perception in music or the like at the same time.

According to the invention, in the speech recognition circuit, the broadcast signal, either the received or the demodulated signal, is statistically evaluated on the temporal and frequency characteristics. Based on the evaluation, a reliable statement can be made as to whether the signal is speech or other signals. If the evaluation shows that the signal is a voice signal, then the pseudo-stereo circuit is disabled.

The pseudo-stereo circuit is always active when the mobile radio receiver due to the broadcast signal broadcast or due to the current local reception conditions is not able to receive a stereo signal in sufficient quality, resulting in automatic switching from stereo to Mono reception of the radio receiver leads. In both cases, the unpleasant sound experience of the flat mono signal automatically, that is upgraded to a pleasant spatial and full sound experience due to the pseudo-stereo sound without complex adjustments, which are associated with a dangerous reduction in attention of the driver for traffic.

This enhancement allows the motorist to always perceive 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 proved 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 mode at a still possible Stereoempfangslage, which automatically leads to a pseudo-stereo signal without necessary influence of the driver to use the pseudo-stereo circuit and thus for processing the mono signal. In this case, the limit is chosen so that a always trouble-free, especially a non-interference reception is certainly possible. It is possible to choose the limit value in each case adapted to the field of application of the mobile radio receiver.

Preferably, a switching unit is provided, which controlled by the quality of the received signal 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 switches.

According to a further feature of the invention, it is proposed to carry out the switching operation in a period of less than 100 ms, with the result that the pure switching operation can not be perceived by the relatively sluggish human ear, since there are regular gaps in the reception of a length below does not notice this time span. This inventive design makes it possible to disguise the pure switching and thus almost conceal the listener.

An alternative embodiment of the invention shows the switching operation in the form of a cross-fade, which is completed within a period of the order of a second. The crossfading is continuous and not abrupt, 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 in this case to get used to the listener to the opposite to the initial state changed final state, which, despite sophisticated pseudo-stereo circuits, although only in slight differences, but still exists. This soft crossfading thus represents an optimized and for the listener very pleasant form of switching.

An advantageous embodiment of the invention results from the combination of the two different Umschaltprinzipien by the transition from stereo to pseudo-stereo reception, the crossfading is applied and in the transition from pseudo-stereo to stereo reception, the switching comes in less than 100 ms to fruition , In this special form, it is possible to slowly get the listener accustomed to the worse pseudo-stereo experience, which makes the usual inconspicuous and thus very pleasant transition to the poorer sound itself. On the other hand, the fast, hard way of switching from bad to better stereo reception is deliberately chosen, since the advantage of stereo reception is particularly noticeable given a sufficiently advantageous sound experience during switching. This combination thus makes it possible to combine the seemingly reluctant switching principles into a particularly advantageous overall device which enables a sound-optimized switching back and forth of the radio receiver from stereo to pseudo-stereo reception.

Preferably, the switching operation is performed according to a predetermined switching characteristic. The switching characteristic is chosen so that the listener perceives the most pleasant switching from one state to another. Examples of suitable characteristics are, but are not limited to, linear gradients or such third degree.

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. The one circuit contains a delay element, on the one hand the input signal and on the other hand, the amplified by a factor g and fed back delayed signal is supplied. The signal delayed in the delay element by the time delay del is subsequently amplified again by the factor -g before it is supplied to the input signal and fed to the output for this channel. The other circuit for the other channel corresponds in structure to the former, it being noted that instead of the gain factor g the factor -g and vice versa is set. This simple type of pseudo-stereo circuit makes it possible to produce a spatial sound sensation close to the stereo signal in a low-cost manner.

In an alternative, further simplified embodiment of the pseudo-stereo circuit, the mono signal is supplied to a delay element which delays them by the time del. Subsequently, this signal is amplified in an amplifier stage by the gain factor g, which lies between 0 and 1. The delayed and amplified signal is subsequently supplied to the two separate circuits for the left and right channels, where it is linked in a respective mixer with the mono signal amplified by the factor g * = 1-g or g ** = g-1. The linked signals then form the output signals for the left and right channel, respectively. This further simplified circuit, with comparable spatial resolution due to the increased use of common components for the two circuits, results in less circuitry, which is reflected in lower susceptibility and lower cost.

According to a further feature of the invention, the time del and / or the factors g are selected such that the user experiences 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 representation 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,

Show it

Fig. 1

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 this reports the presence of a stereo or a mono signal. The signal output by the stereo decoder is supplied on the one hand to a switching unit and on the other hand supplied to a pseudo-stereo circuit, which processes the supplied signal to a pseudo-stereo signal and subsequently supplies the switching unit. The switching unit switches controlled by the Control Unit between the supplied signals back and forth. If the stereo decoder recognizes 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 switching 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 of a mono signal. The switching process is carried out according to switching characteristics permanently stored in the switching unit, wherein preferably a "hard" switching with a time of less than 100 ms of pseudo-stereo to stereo and a "soft" switching in the form of a fade over a period of the order of one second is selected. It does not matter for what reason the mono signal has arisen, ie it is independent of whether only a mono signal was received or received due to the poor reception conditions of the stereo signal this only as a mono signal and amplified.

Although not in Fig.1 As shown, the mobile broadcast receiver includes a voice recognition circuit for inhibiting the processing when speech is present.

Speech recognition is performed by a static evaluation of the union or frequency course of the Aundfunksignals.

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

In the circuitry simpler circuitry in Fig. 3 the mono signal is delayed by a time del in a delay element common to both circuits and amplified by a factor g in a common amplifier stage which is between 0 and 1. This delayed and amplified mono signal is then fed to the two circuits for the left and the right channel, respectively, where in each mixer stage with the amplifier stage arranged in each circuit by the factor g * = 1-g or g ** = g-1 amplified mono signal is linked and the respective output channel of the pseudo-stereo circuit is supplied.

Claims (11)

1. A mobile radio receiver with the following features:

   - an FM tuner with a stereo decoder, on whose output a stereo or mono signal may be taken off;

   - a pseudostereo circuit, which is connected to the output of a stereo decoder,

   - a quality evaluation circuit, by which, when the reception quality falls below a threshold value, switching over from stereo operation to mono operation may be effected and thereafter the processing into a pseudostereo signal may be initiated,

   - a speech recognition circuit, by which, when speech is present in the received signal, processing of the mono signal into a pseudostereo signal may be prevented,

   wherein the speech recognition circuit includes an analysis circuit for the temporal or frequency pattern of the radio signal, which receives the pattern, statistically analyses it and supplies the result of the analysis to the pseudostereo circuit.
2. A mobile radio receiver as claimed in Claim 1, characterised in that the threshold value is so selected that there is early switching over to mono operation, even when stereo reception sufficiently low in interference is still possible.
3. A mobile radio receiver as claimed in one of the preceding claims, characterised in that a switchover unit is provided, by means of which switching over between the stereo signal and the pseudostereo signal from the pseudostereo circuit may be performed.
4. A mobile radio receiver as claimed in Claim 3, characterised in that the switchover unit is so constructed that the switchover process is terminated in less than 100 ms.
5. A mobile radio receiver as claimed in Claim 3, characterised in that the switchover unit is so constructed that the switchover process in the form of cross-fading is terminated within a period of time of about 1s.
6. A mobile radio receiver as claimed in Claim 4 and 5, characterised in that the switchover unit is so constructed that the switchover process to pseudostereo in the form of cross-fading is terminated within a period of time of about 1s and that the switchover process from pseudostereo to stereo is terminated in less than 100 ms.
7. A mobile radio receiver as claimed in one of the preceding claims,
   characterised in that the pseudostereo circuit for the two stereo channels (L, R) have a respective separate switching circuit, which includes a delay element, to the input of which the output signal from the delay element, which is linked to the mono signal and is amplified by a factor g and fed back, is supplied and the output signal of which is amplified by the factor -g and is then again linked to the mono signal, wherein the factor g is selected to be positive for the first stereo channel (L) and the factor g is selected to be negative for the second stereo channel (R).
8. A mobile radio receiver as claimed in one of the preceding Claims 1 to 6, characterised in that the pseudostereo circuit has a respective separate switching circuit for the two stereo channels (L, R), in which a mixer is provided, which links the mono signal, which has been delayed by a delay element by a delay time (del) and has been amplified by an amplifier stage by g (0<g<1) with the non-delayed mono signal which has been amplified for the one channel by g*=1-g and for the other channel by g**=g-1 and supplies it to the respective channel output.
9. A mobile radio receiver as claimed in Claim 7 or 8, characterised in that the factor g is adjustable.
10. A mobile radio receiver as claimed in one of Claims 7 to 9, characterised in that the delay time (del) is adjustable.
11. A mobile radio receiver as claimed in one of the preceding claims, characterised in that the circuit for the recognition of speech includes a detector for the recognition of traffic reports, which is connected to the pseudostereo circuit and which prevents processing when traffic reports are present.

Images