Method for reducing the effect of impulse noise in a motor vehicle radio

Methods are provided for reducing impulse noise effects in a motor vehicle radio. One method includes the steps of first detecting impulse noise received by the motor vehicle radio. The received impulse noise is classified as either short pulse width impulse noise or as long pulse width impulse noise. The short pulse width impulse noise can generally be blanked without seriously affecting the audio quality of the radio. For the long pulse width impulse noise, a maximum long pulse width blanking repetition rate is set and such impulse noise pulses are blanked at a blanking rate less than the maximum long pulse width blanking repetition rate.

TECHNICAL FIELD

The present invention generally relates to a motor vehicle radio, and more particularly relates to reducing the effect of impulse noise in a motor vehicle radio with minimum impact on the audio quality of the sound produced by the radio.

BACKGROUND

A motor vehicle is a noisy environment for radio reception. Impulse type noise, for example, is a particularly troublesome source of interference to motor vehicle radio reception. There are multiple sources of impulse type noise in a motor vehicle. Some of the noise sources, such as brake switches and turn signals, produce impulse noise pulses that individually are characterized by a relatively low repetition rate and a relatively long pulse width. In contrast, other sources such as the ignition system produce impulse noise pulses that are of relatively short pulse width. Ignition system noise is characterized by a variable repetition rate, with the rate changing with the engine speed.

A conventional motor vehicle radio attempts to eliminate the effect of impulse type noise by blanking such noise signals. If the radio attempts to blank all noise signals, however, the effect of such blanking may be discerned by the listener as a distorted audio signal. If, however, sufficient blanking is not applied, the audio quality is again impaired because the normal audio is punctuated by pops or cracks caused by the noise signals. In an attempt to provide sufficient blanking but not to over-blank, the typical motor vehicle radio sets a fixed maximum blanking time and a fixed repetition rate. Such typical settings, however, are sub-optimized for dealing with the different noise sources. The result is sub-optimized audio reception on motor vehicle radios.

Accordingly, it is desirable to provide a method for reducing the effect of impulse noise in a motor vehicle radio to optimize the audio quality of motor vehicle radio reception. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

BRIEF SUMMARY

Methods are provided for reducing impulse noise effects in a motor vehicle radio. One method includes the steps of first detecting impulse noise received by the motor vehicle radio. The received impulse noise is classified as either short pulse width impulse noise or as long pulse width impulse noise. The short pulse width impulse noise can generally be blanked without seriously affecting the audio quality of the radio. For the long pulse width impulse noise, a maximum long pulse width blanking repetition rate is set and such impulse noise pulses are blanked at a blanking rate less than the maximum long pulse width blanking repetition rate.

DETAILED DESCRIPTION

FIGS. 1-3graphically illustrate examples of impulse noise spectrum that may be experienced in a motor vehicle radio receiver. The impulse noise spectrum is shown superimposed on an illustrative received radio signal8. In each ofFIGS. 1-3vertical axis10indicates signal magnitude and horizontal axis12indicates time. It is well known that impulse noise pulses can be blanked by a motor vehicle radio. Blanking is the act of blocking transmission of a portion of the spectrum received by the radio tuner. The act of blanking a noise impulse also blanks the radio signal received simultaneously with the noise impulse. Excessive blanking of noise signals will blank or cut out a noticeable amount of the received radio signal and such excessive blanking will be perceived by the listener as a distortion of the received signal.

FIG. 1illustrates a plurality of short pulse width impulse noise pulses14superimposed on illustrative received radio signal8. As used herein the term “short pulse width” shall mean a pulse width of less than about 200 nanoseconds (ns). Such short pulse width impulse noise pulses can usually be effectively blanked without causing significant deterioration of received radio signal8because only a small portion of the received radio signal is blocked.

FIG. 2illustrates a plurality of long pulse width impulse noise pulses16superimposed on illustrative received radio signal8. In this illustrative figure the impulse noise pulses occur at a low repetition rate. Long pulse width impulse noise pulses occurring at such a low repetition rate also can effectively be blanked without causing significant deterioration of received radio signal8, again because only a small portion of the received radio signal is blocked.

FIG. 3again illustrates a plurality of long pulse width impulse noise pulses18superimposed on illustrative received radio signal8. In contrast to the previous figure, however, noise pulses18occur at a high and not necessarily regular repetition rate. Long pulse width impulse noise pulses such as noise pulses18that occur at a high repetition rate cannot all be blanked without causing a significant deterioration in the audio quality perceived by a listener of the motor vehicle radio. Blanking all long pulse width impulse noise pulses18will cause the blocking of a significant portion of the received radio signal and such blanking will be perceptible to the radio listener.

FIG. 4illustrates, in flow chart form, a method in accordance with an embodiment of the invention by which the blanking of impulse type noise can be optimized in a motor vehicle radio. The basic process of blanking noise pulses in a radio is known to those of skill in the art and need not be explained. Steps contemplated in the inventive method can be carried out in the tuner section of the motor vehicle radio and more specifically in the tuner IF section of the motor vehicle radio.

As illustrated inFIG. 4, the method in accordance with one embodiment of the invention starts at step20. At this point the motor vehicle is generally running and the motor vehicle radio is turned on and tuned to a radio station. At step22impulse noise pulses received by the radio are detected. The impulse noise pulses are detected by the radio tuner and are distinguished from the spectrum of the selected radio station. In accordance with this embodiment of the invention, at step24the impulse noise pulses are classified as either short pulse width impulse noise pulses or long pulse width impulse noise pulses. As used herein, the term “long pulse width” shall mean a pulse width greater than about 200 ns. The definition of “short pulse width” and “long pulse width” may depend on the particular motor vehicle radio, but for most applications a demarcation of about 200 ns is appropriate. The classification of the received impulse noise pulses can be done in the tuner of the motor vehicle radio, and especially in the tuner IF section of the radio. Digital IF tuners are particularly suited for the classification of the received impulse noise pulses.

In accordance with one embodiment of the invention, short pulse width impulse noise pulses are blanked as indicated by step26. Preferably all such short pulse width impulse noise pulses are blanked as total blanking of such pulses can generally be done without significantly impacting the perceived radio reception quality. The blanking of long pulse width impulse noise pulses is limited to a predetermined maximum long pulse width blanking repetition rate. The maximum long pulse width blanking repetition rate, which can be set in the tuner of the motor vehicle radio, can be set to be any predetermined number of blankings per second with the exact predetermined number based on factors such as the particular radio and the motor vehicle environment (i.e., for example, the particular model of automobile in which the radio is installed). As indicated at step28, with respect to long pulse width impulse noise pulses, a determination is made as to whether blanking has been done within a time window established by the predetermined maximum long pulse width blanking repetition rate. The time window is the period of the maximum long pulse width blanking repetition rate. Upon receipt of an impulse noise pulse that is classified as a long pulse width impulse noise pulse, if previous blanking has been done within the time window, that noise pulse is not blanked as indicated by step30. If, instead, previous blanking has not been done within the time window, that noise pulse is blanked as indicated at step32. By limiting the blanking of long pulse width impulse noise pulses to a repetition rate less than the predetermined maximum long pulse width blanking repetition rate, impulse type noise is reduced, but audio quality of the received broadcast is not severely impacted.

In accordance with one embodiment of the invention, the short pulse width impulse noise pulses are blanked for a blanking time commensurate with the pulse width. Long pulse width impulse noise pulses are blanked for a longer blanking time.

In accordance with a further embodiment of the invention, the motor vehicle radio includes either a timer or a counter. As illustrated inFIG. 5, following the classification done at step24, the first detected long pulse width impulse noise pulse is blanked at step40and simultaneously the counter or timer is started at step42. Upon detection of a further long pulse width impulse noise pulse at step44, the timer or counter is consulted at step46to determine whether the previous blanking has been done within the predetermined time window. The timer or counter is reset as indicated by line48and the detected long pulse width impulse noise pulse is either blanked, step32, or not blanked, step30, based on the determination of whether the previous blanking has been done within the predetermined time window. That is, the steps of blanking or not blanking are done based on whether the timer has exceeded a predetermined time or the counter has exceeded a predetermined count. A counters and a timer function in much the same way in this application, with the difference generally being merely a choice of the most convenient way to implement the function in a portion of the integrated circuit that makes up the tuner portion of the motor vehicle radio. Accordingly, the function and its predetermined setting will hereinafter simply be referred to as a timer and a predetermined time, respectively.

In accordance with one embodiment of the invention, all short pulse width impulse noise pulses are blanked and long pulse width impulse noise pulse are either blanked or not blanked based on the maximum long pulse width repetition rate as explained above. In accordance with a further embodiment of the invention (not illustrated), short pulse width impulse noise pulses may also be blanked or not blanked based upon a maximum short pulse width blanking repetition rate in a manner similar to that described for long pulse width impulse noise pulses. In accordance with this embodiment of the invention, the maximum short pulse width blanking repetition rate can be greater than the maximum long pulse width blanking repetition rate because the blanking time for a short pulse width impulse noise pulse is less than the blanking time for a long pulse width impulse noise pulse and thus has less effect on the perceived audio quality of the received radio broadcast. As with the maximum long pulse width blanking repetition rate as explained above, the maximum short pulse width blanking repetition rate can be set to be any predetermined number of blankings per second with the exact predetermined number based on factors such as the particular radio and the motor vehicle environment. The maximum short pulse width blanking repetition rate can be, for example 2000 blankings per second.