JL Audio's success in car audio largely results from their continual drive to make products that are both innovative and in tune with the market. Although they have primarily manufactured subwoofers and amplifiers rather than source units, processors or electronics, JL Audio's product development team saw the increasing number of vehicles with fully integrated source units (which make installing an aftermarket source unit extremely challenging and costly) as an opportunity to create a new product.
From a sound-quality perspective, the biggest challenge of trying to integrate with recent OEM source units has been extracting a quality audio signal with flat frequency response to feed into aftermarket amplifiers and speakers. Car manufacturers have been quick to adopt audio systems with digital signal processing that allow their engineers to "optimize" the sound behind the scenes with equalization that cannot be adjusted or defeated. Although this may be great for the factory sound system with factory speakers, it quickly becomes a problem when trying to integrate aftermarket audio products and make them sound good. While some factory systems still have unequalized or mildly equalized audio outputs that may have acceptable sound quality when interfacing with aftermarket amps and speakers, many use quite drastic equalization curves to try to level out the poor frequency response of cheap factory speakers. JL Audio's CleanSweep CL441DSP is the first OEM audio interface on the market that addresses the issue of imbedded equalization in many of today's vehicles.
The most unique feature of the CL441SDP is its 32-bit SHARC DSP processor that allows it to automatically "unequalize" the uneven frequency response of the factory audio signal through four channels of 30-band equalization. Some may argue that it is possible to interface an aftermarket equalizer (with the use of a real time analyzer) and perform the same task, but the CL441DSP automatically flattens the frequency response to +/- 1 dB in approximately 20 seconds if you simply insert the calibration CD into the factory source unit, turn up the volume to 3/4 volume and press a button. I think it would be safe to bet that even the world's fastest audio tuner wouldn't be able to beat the CleanSweep unit. Each channel is independently equalized to deal with systems that have different equalization curves for front and rear outputs.
The "flattened" audio output is converted back to the analog domain and output in the form of 8-volt RMS pre-amp outputs. Just to clarify, the CleanSweep is designed to create an electrical signal output with "flat" frequency response, just as an aftermarket head unit would, not to make the tonal balance of an aftermarket audio system (what you hear) sound "flat." The input level setting of the CL441DSP is also fully automatic, so whether you feed it low-voltage pre-amp-level signal or high-power amplified speaker-level signal, it compensates automatically and provides an 8-volt RMS pre-amp output.
After installing a CleanSweep unit, there are two ways to operate the volume. The first option is with the factory volume knob/steering wheel controls, just as it came from the factory. While this may be the most user-intuitive way, some factory audio systems incorporate volume-dependent equalization curves, and the CL441DSP cannot fully compensate for factory equalization when the curves vary with volume. The good thing is that many volume-dependent equalizer effects can be minimized (through the factory radio settings) and the volume-dependent curves are usually variations in bass response from the baseline equalization curve. This means that the "flattened" response provided by the CleanSweep at 3/4 volume will be in the ballpark throughout most of the frequency response even at 1/4 or full volume.