This invention relates to sound processing and more particularly to digital sound processing and equalization of audio signals for vehicle audio systems.
The design of audio systems for vehicles involves the consideration of many different factors. The audio system designer selects the position and number of speakers in the vehicle. The desired frequency response of each speaker must also be determined. For example, the desired frequency response of a speaker that is located on the instrument panel may be different than the desired frequency response of a speaker that is located on the lower portion of the rear door panel.
The audio system designer must also consider how equipment variations impact the audio system. For example, an audio system in a convertible may not sound as good as the same audio system in the same model vehicle that is a hard top. The audio system options for the vehicle may also vary significantly. One audio option for the vehicle may include a basic 4-speaker system with 40 watts amplification per channel while another audio option may include a 12-speaker system with 200 watts amplification per channel. The audio system designer must consider all of these configurations when designing the audio system for the vehicle. For these reasons, the design of audio systems is time consuming and costly. The audio system designers must also have a relatively extensive background in signal processing and equalization.
Consumer expectations of vehicle sound quality have dramatically increased over the last decade. Consumers now expect a very high quality sound system in their vehicles. In addition to high-quality audio from conventional sources such as radios, compact discs, and tape players, vehicle audio systems are being integrated with cellular phones, navigation systems, and video systems. Each of these additional audio sources have channel inputs and audio processing requirements that may be different than the stereo head unit. Some vehicle audio systems employ advanced signal processing techniques to customize the listening environment. For example, some vehicle audio systems incorporate matrix surround sound processing that is similar to surround sound offered in home theater systems.
Surround sound processors combine the left and right input signals in different proportions to produce two or more output signals. The various combinations of the input audio signals may be mathematically described by a Nxc3x972 matrix. The matrix includes 2N matrix coefficients that define the proportion of the left and/or right input audio signals for a particular output signal. In the more general case, surround sound processors can also transform N input channels into M output channels using a Nxc3x97M matrix of coefficients. U.S. Pat. Nos. 4,796,844 and 5,870,480 to Greisinger, which are hereby incorporated by reference, disclose a surround sound system that provides 5 or 7 channels from left-right stereo inputs.
As can be appreciated from the foregoing, a sound processing and equalization design tool that assists audio system designers in integrating multiple audio sources would be desirable. Sound processing and design tools that allow audio system designers to create custom sound processing and equalization for vehicle audio systems would also be desirable. It would also be desirable to reduce the level of experience and the time required to design the vehicle audio systems.
A digital sound processing design system for a vehicle audio system according to the invention includes a computer and a design tool that is run by the computer. The design tool allows a user to define sound processing criteria that is stored in a template file. An audio signal processor is connected to first and second real channel inputs of an audio source. Memory that is coupled to the audio signal processor stores the template file. The sound processing engine that is coupled to the audio signal processor and the memory reads the template file at run-time to obtain the sound processing criteria. The sound processing engine applies the sound processing criteria to the first and second real channel inputs. The design tool allows a user to create virtual channel inputs and outputs that are based, in part, on the first and second real channel inputs.
In still other features of the invention, the sound processing criteria includes a speed/gain function that various a gain factor of at least one input channel as a function of vehicle""s speed. Filter profiles can also be applied to at least one of the first and second real channel inputs. Other sound processing criteria include channel gain, vehicle identification selectors, audio source selectors, delay, etc.
Still other objects, features and advantages will be apparent to skilled artisans after reviewing the specification, the drawings, and the claims that follow.