Method and apparatus for adjusting tone in a sound system

Abstract: A vehicle radio (10) having a microprocessor based control (10) has bass and treble tone controls (22,24) and a fade control (26) to produce digital settings. A tone adjusting arrangement compensates for the effect of fade change on perceived tone or frequency response. Tables of compensation values stored in a ROM (32) and addressed by fade settings are used to change the nominal tone settings. The tone setting combined with the compensation value provides an adjusted or compensated tone value to maintain a consistent tone when fade is adjusted.

Description: This invention relates to a method and apparatus for compensating for the effect of an adjustment in fade in a vehicle sound system. Sound systems installed in automotive vehicles are typically equipped with controls for adjusting tone, either by bass and treble controls or by multi-channel equalizers, to adjust the sound characteristics to the preference of the operator. Thus a certain amount of balance of frequency ranges is attained. Where the vehicle is equipped with front and rear speakers, a fade control is used to apportion the sound volume between the front and rear. When fade is changed, the balance of the frequency ranges is often changed as well, depending on the acoustical response characteristics of the vehicle. This causes the operator to adjust the bass/treble settings manually upon each fade operation to maintain a consistent sound. To overcome drastic changes in the frequency response due to fade changing it is sometimes attempted to design a "flat" response in a given style of vehicle by redesign of speakers, the acoustical housing, electronic hardware, and speaker location. Such customizing is expensive and takes considerable time. Present vehicle radio systems tend to use microprocessor control technology and thus have the capability of calibrating various functions by software design. It is desirable then to use software calibration rather than hardware changes to customize the frequency response of a system for a given vehicle to meet user expectations thereby achieving a new level of flexibility in audio system design at minimal or no extra expense. Of course, hardware changes could be made, for example by a circuit in integrated form. The present invention seeks to provide an improved method and apparatus for adjusting tone in a sound system. According to an aspect of the present invention, there is provided an apparatus for compensating for the effect of an adjustment in fade in a vehicle sound system as specified in claim 1. A preferred embodiment is carried out in a vehicle sound system having front and rear speakers and a fade control to apportion the sound volume between front and rear, the bass and treble response at a given location in the vehicle being subject to change due to the fade adjustment, comprising a circuit for operating speakers; manually operated tone control input means for selecting a tone setting; manually operated fade control input means for selecting a fade setting; a microprocessor control for the circuit responsive to tone and fade settings, the control including tables of tone compensation values addressed by fade setting, whereby for each fade setting the control identifies compensation values and outputs a tone control signal as a function of the tone settings and the compensation values. According to another aspect of the present invention, there is provided a method of compensating for the effect of an adjustment in fade in a vehicle sound system as specified in claim 7. A preferred embodiment is carried out in a microprocessor controlled vehicle sound system having front and rear speakers, a tone control generating tone settings, and a fade control generating a fade signal to apportion the sound volume between front and rear, the tone at a given location in the vehicle being subject to change due to the fade adjustment; the method of compensating for the effect of fade adjustment comprising the steps of providing tables of compensation values addressed by fade settings; sampling the fade signal; looking up compensation values for the fade setting; combining the compensation value with the tone settings to derive an adjusted tone signal; and controlling the speakers in accordance with the fade setting and the adjusted signal. An embodiment of the present invention is given below, by way of illustration only, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a typical vehicle radio system adapted for use with an embodiment of the present invention; Figure 2 is a schematic diagram of a microprocessor and controls for use in the system of Figure 1 with provision to accommodate an embodiment of the invention; Figure 3 is a graph illustrating the effect of fade position on compensated tone setting according to an embodiment of the invention; and Figures 4 and 5 are flow charts illustrating the programs used to carry out an embodiment of the invention. Referring to Figure 1, an automotive radio system includes a control head 10, a radio module 12 which is coupled to the head 10 by a data bus 14, an antenna 16 coupled to the module 12 and left and right speakers 18 and 19, respectively, also connected to the module. The module 12 or radio receiver has circuitry controlling the speakers in accordance with commands initiated at the head 10. The tuning of the module 12 as well as volume, bass, treble, fade and balance or other functions is controlled by the head 10 which sends control signals to the module 12 in the form of digital data via the bus 14. The head includes control knobs 20 - 26 or buttons for manual selection of each function and a display 28 which is used to show at least the chosen radio frequency but may also graphically depict the volume, bass/treble settings and fade setting, in addition to time. It should be understood that tone control other then bass/treble controls may be used; for example, a multi-channel equalizer may provide the tone settings. Digital signals carried by the bus 14 communicate to the module 12 any settings or changes which input by adjustment of knobs 20-26. The signal for fade control, for example, is a number from 0 to 63, with high numbers corresponding to a higher volume at the rear speakers and low volume at the front speakers. Thus, by changing the digital fade signal, the head 10 commands the module 12 to change the front and rear volume accordingly. The same method is used for control of tone, or bass/treble settings. The digital signals for either bass or treble are numbers from 0 to 15, with 15 providing the greatest emphasis for that frequency range. The head 10 and the module 12 each have a microprocessor programmed to manage the head function and module function, respectively, as well as the communications over the bus 14. The signals sent by the head 10 to the module 12 may be of two types; either a number for a setting, which the module 12 must conform to, or a command to increment or decrement the existing setting. After executing a command from the head 10, the module 12 sends a status report over the bus 14 to indicate the new value. Figure 2 shows the microprocessor 30 for the head 10 which has inputs from the control knobs 20-26 and inputs as well as outputs on bus 14. A read only memory (ROM) 32 permanently stores certain control parameters for use by the microprocessor, while a read/write memory (RAM) 34 is used for calculations and to store variables. A portion of the RAM 34, called a "keep alive" memory, is maintained even when the vehicle ignition is turned off by supplying voltage from the vehicle battery. The selected radio settings are stored in the "keep alive" memory so that when the ignition is turned on the radio settings will be the same as when the vehicle was last used. To compensate the tone for changes in fade, the microprocessor 30 is programmed to adjust the tone for the fade setting. By empirically making such adjustments in a vehicle, a table of desired adjustments for the desired compensation can be compiled and stored in the ROM 32. Different tables may be used for bass settings and treble settings, and indeed different sets of tables could be used for various conditions such as high or low tone settings. A typical table is as follows: The effect of tone compensation according to this table is shown in Figure 3 which shows the bass or treble setting on the ordinate and the fade position on the abscissa. A normal bass or treble level is three as shown by a horizontal line at that level. The tone is compensated at each fade setting according to the above table, resulting in the stepped function shown by cross-hatching. Since the tone setting is three in this example, the boost of -4 is ineffective at the lowest fade settings. In this case, the same compensation table is used for bass and treble but a different table can be used for each one. The flow chart of Figure 4 represents a routine which is used to detect a change in fade setting, to look-up the proper boost amount, and if the boost amount is different, to send a new tone setting to the module 12. The program is run for treble compensation and then for bass compensation, but the bass/treble designation is used in the chart. In the flow chart description, the reference numerals nn on the blocks are used in angle brackets <nn> to refer to the functions of the blocks. Here, it is assumed that a fade setting change was sent to the module 12, the change was executed and the new fade setting was reported back to the head 10. In the compensation program, the fade setting message is read <40>, and compared to the old setting <42>. If the setting is the same, the program ends, but if it is different, the setting is stored <44> for use in the next execution of this routine. Then the new compensation is looked up in the ROM table <46> and if it is the same as the old compensation value <48>, the program ends but if it is different, the new value is stored <50> and the bass or treble message is set to a new level <52> by summing the tone setting with the new compensation value, and sent over the bus 14 to the receiver module <54>. In the receiver module, as shown in the flow chart of Figure 5, the messages to change fade setting and the compensated bass or treble setting are received and stored <56>, the radio function is executed pursuant to the message <58>, and messages of the resultant fade or tone status are sent to the head <60>. It will thus be seen that the tone setting is readily adjusted or compensated for changes in fade and that the compensation program applies to any number of channels or frequency ranges that are subject to adjustment. It will be apparent that the invention applies to any microprocessor controlled sound system as covered by the claims and is not limited to one having a separate head and receiver module. That is, an integrated radio unit can utilize the same program for tone compensation.

Claims: Apparatus for compensating for the effect of an adjustment in fade in a vehicle sound system which includes front and rear speakers (18,19), sound being apportionable by fade control between the front and rear speakers, the proportions of bass and treble components of the sound at a given location in the vehicle being subject to change due to the fade control; the apparatus comprising a drive circuit (12) for operating the speakers (18,19); tone control means (22,24) for selecting a tone setting; fade control means (26) for selecting a fade setting for use in apportioning sound between the front and rear speakers; processing means (30) for controlling the drive circuit on the basis of the selected tone and fade settings, the processing means (30) being adapted to provide tone compensation values on the basis of the selected fade setting, whereby for each fade setting the processing means (30) is adapted to obtain a compensation value and to output a tone control signal as a function of the selected tone setting and the obtained compensation value. Apparatus according to claim 1, wherein the tone control means (22,24) comprises a bass control and a treble control for selecting bass and treble tone settings; the processing means being adapted to obtain separate bass and treble compensation values. Apparatus according to claim 1, wherein the tone control means (22,24) comprises controls for a plurality of discrete frequency ranges, each control being adapted to select a tone setting for a respective frequency range, the processing means being adapted to obtain a separate compensation value in respect of each frequency range. Apparatus according to claim 1, 2 or 3, comprising one or more tables of compensation values, the processing means being adapted to obtain the or each compensation value from the or each associated table on the basis of the selected fade setting. Apparatus according to any preceding claim, wherein the or each tone setting and the or each obtained compensation value is in the form of a digital value, the processing means being adapted to sum the or each compensation value with the associated tone setting, thereby determining the tone control signal. Apparatus according to any preceding claim, wherein the tone control means (22,24) and the fade control means (26) are manually operable. A method of compensating for the effect of an adjustment in fade in a microprocessor (30) controlled vehicle sound system which comprises front and rear speakers (18,19), tone control means (22,24) for generating a tone setting and fade control means (26) for generating a fade signal adapted to apportion the sound between the front and rear speakers (18,19), the proportions of bass and treble components of the sound at a given location in the vehicle being subject to change due to the fade control; the method comprising the steps of sampling the fade signal; obtaining a compensation value on the basis of the fade signal; deriving an adjusted tone signal on the basis of the tone setting and the obtained compensation value; and controlling the speakers (18,19) on the basis of the fade setting and the adjusted tone signal. A method according to claim 7, comprising the steps of storing previous values of the fade signal and the tone setting; comparing the sampled fade signal with the previous fade signal to detect the occurrence of a fade change; a compensation value and an adjusted tone signal being obtained on the occurrence of a fade change on the basis of the sampled fade signal. A method according to claim 7 or 8, comprising the step of providing a table of compensation values addressable on the basis of the fade signal. A method according to claim 7, 8 or 9, wherein separate tone settings are provided for each of a plurality of frequency ranges; the method comprising the step of providing a table of compensation values for each frequency range.

Inventors: MORSE DALE LAVERNE, SANDERS ERIC ALLEN, MORSE, DALE LAVERNE, SANDERS, ERIC ALLEN
Applicants: DELCO ELECTRONICS CORP, DELCO ELECTRONICS CORPORATION
Application year: 1992
Main classification: H04R5
IPC codes: H03G5, H04R3, H04S7, H03G9