OEM Integration

A voice from America

OEM Audio Integration – The Basics

By Todd Ramsey

The original equipment parts in a vehicle, including its in-dash electronics (infotainment system), are referred to as OEM or “Original Equipment Manufacturer” in the automotive world. Replacing OEM infotainment electronics in modern vehicles is not necessary to gain improved sound. The trend for integrating infotainment systems into the dashboard began in the mid-1990s with luxury vehicles. It didn't take long for aftermarket installers to work out that improving a vehicle’s sound system can be accomplished without removing them. In many cases today, this is the preferred option.

If the factory-supplied electronics meet your connectivity and functionality needs, there is little need to consider removal to improve overall audio playback quality. Interfacing factory-supplied infotainment systems to aftermarket sound systems is referred to as OEM audio integration. There are many solutions to accomplish this depending on the nature of the upgrade and the year/make/model/trim level of vehicle. The solutions include a mix of aftermarket products and professional installation services.

What to Consider?

The first consideration in any automotive sound system enhancement is what you like and don’t like about the current audio system’s performance. Here are some common evaluation points to consider while listening to well-recorded, dynamic music:

·      Do you like the accuracy of the system’s frequency range and does it seem balanced? This relates to how realistic and complete a piece of music sounds along with the balance of frequencies. No range of frequencies should either dominate or be missing. Is there enough bass? Is it too dominant in the mid range? Is it lacking openness and clarity of high frequency reproduction?

An obvious upgrade for some is to add a subwoofer. Some vehicles have two or three-way component speakers that can be replaced. However, if the realism and balance of frequency response is lacking – especially where the vehicle already has factory-supplied component speakers – adding equalisation and frequency response correction will help that balance and fine-tuning significantly. Any aftermarket speaker upgrades and subwoofer additions will be able to get the fine-tuning required to have a balanced frequency response.

·      Soundstage - Do you like the position of the sound elements? Does it capture a sense of space? This is not about how true to life the sound of the instruments or voices are, rather it’s about from where in the vehicle (typically the front cabin area) they are positioned. How do you like the vocal placement relative to other instruments? Do instruments seem spread out to be discernable and believable with a centred vocal, or do they sound as if coming only from one place – such as the side on which you’re sitting? Does the sound have the illusion of emanating from a space larger than the cabin?

“Side-biasing” is a common problem because in vehicles no listener sits directly in the middle. Thus, you often hear the right side louder than the left if seated on the driver’s side. If the vehicle does not have good left-to-right balance, an integration processor with time correction capabilities allows the sound in the nearer channel to be delayed so that the primary listener has an optimised soundstage that appears as if seated in the middle. The time correction capabilities in a DSP-based processor can be adjusted to correspond with other presets that suit different situations, such as with and without a front seat passenger.

If the vehicle does have a good left-to-right distribution of sound with minimal side-biasing), has good spatial cues (seems like a larger space) and you like it, there may be an upmixer in the factory sound system. An upmixer takes a two-channel signal and provides specific treatment to front and rear channels to simulate the effect of a larger space, as well as positioning of level and bandwidth-specific frequencies to better position a front sound stage. Often vehicles with upmixers have a centre channel speaker to assist with these goals. You can still improve the frequency response and other aspects of these systems, but preserve the upmixer to ensure the positioning of sound remains, as you already like it. Many DSP-based integration processors allow configurations for retaining any channel-specific factory features like an upmixer.

·      Does it sound clear and undistorted at your chosen listening level? Audible distortion at around normal conversation levels suggests the sound system lacks sufficient power. It can also indicate other things such as a need for more comprehensive equalisation and/or higher fidelity speakers. This is relative to the volume level. If you listen at relatively low volumes and it is not clear or seems distorted, be sure to flatten any tone controls before making a final assessment.

Unclear, distorted sound is evidence of needing more amplification. How much depends on the speakers to which the amplifier channels will connect. In addition, if the vehicle lacks quality speakers and a subwoofer, those areas would need to be addressed to make the most of any amplifier upgrade. Of course ensuring that the signal from the OEM system is clean and undistorted is paramount to a successful outcome.

Two General Approaches

There are two general approaches to integrating with an OEM system in pursuit of better sound. Even if the equipment (such as DSP-based processor or multi-channel amplifier) performs other functions, it’s only at the point of interface where the two approaches are categorised.

1)    Using Vehicle-Specific Interface Devices – These offer reverse-engineered approaches allowing a factory sound system’s CAN-Bus, MOST, D2B, A2B or other data-bus containing audio information to convert to analogue and/or digital audio outputs that connect directly to aftermarket DSP processors and amplifiers.

Some products in this category have built-in signal processing capabilities. Most have useful configurable features such as allowing the factory tone control for bass to operate the subwoofer level of the subwoofer amplifier. Many still require amplifier(s) or other equipment to complete the process of getting the signal to speakers. One big benefit is that the retention of audible safety features like reverse sensor beeps and other warning sounds usually delivered through the speakers are completely preserved in vehicle-specific interfaces. The downside is the availability of vehicle-specific interfaces available.

Example of vehicle-specific interface devices: 1) Audison bit DMI for specific vehicles with MOST 25 optical infotainment-bus systems. 2) Rainbow DSP 1.8 used with optional MOST module for select vehicles.

2)    Using À la Carte Interface Devices – These are not vehicle specific and can be used in a wide variety of applications. Instead of using audio signals from the vehicle data-bus, the audio is captured at the speaker-level outputs – typically at the OEM amplifier.

The appropriate device depends on features, number of input/output channels and complexity of the vehicle system into which it will install. This means a subwoofer upgrade leaving the remaining speakers in place is a different device than, say, a complete multi-channel active DSP-based sound system with front /rear component speakers and a subwoofer that will preserve the upmixer. Some devices can “un-do” much of the sound processing the factory signal has on it, so the output to the aftermarket devices are flat. In this approach, the retention of original audible safety features is entirely possible when correct installation practices are observed.

Example of à la carte interface devices: 1) AudioControl’s LC2i active line converter with AccuBASS for easy amplifier and subwoofer upgrade. 2) Audison bit One HD for a multi-channel aftermarket system upgrade utilizing channel summing, equalization, time-correction, auxiliary inputs and other required features.

Adaptations of the both groups can be offered with vehicle-specific wiring harnesses, multi-channel amplifier(s), adapters for upgraded speakers and/or a suitable subwoofer enclosure to create a package that’s specific to a certain vehicle.

FOUR MASTER specialists are expert in selecting the best solution for your particular car.  All that’s left is to enjoy the drive.

Todd Ramsey is CEO of Ramsey Consulting Group Inc. in America. With many years of in car audio experience, Todd is the undisputed king of OEM integration. Our thanks go to him for supplying this excellent article.