Car Audio, Custom Fabrication, Mobile Electronics

LIS Audio How-To: Choosing Signal Processors and Line-Out Converters


Are you looking to upgrade the factory stereo system, without changing the source unit (radio, navigation system), but don’t have the RCA connections needed to expand the aftermarket sound system? Are you confused as to which type of signal processor, or line-out converter, maybe best for your scenario? When it comes to adding aftermarket amplifiers to a factory source unit (radio), it is important to know which processor will work best for the application at hand. In this blog we will breakdown some the differences in signal processors and line-out converters often used to pull signal from a factory audio system.

This build we did in a 2018 Honda Civic Si is a great example of integrating aftermarket audio while using the factory source unit. Check out the blog 2018 Honda Civic Sub-stage and Dress to see more details.

Do I need a Line-out Converter?

I will attempt to cover a many of the key points to help give a better understanding as to why a Line-out Converter, or Signal Processor, maybe necessary when upgrading. Some aftermarket amplifiers will offer a built in line-out converter option, often referred to as “high-level” or “Speaker Level” inputs. This will typically be in the form of a 4-16 Pin plug/s that are labeled to be connected to the factory speaker, or signal source, leads. The amount of pins, and wires needing to be tapped for signal, will depend on the amplifiers setup and goals of the overall system. These “onboard” line-out converters are not typically great quality and tend to offer an audibly weak signal, when compared to using a line-out converter to RCA combination.

A 370Z that received a basic sub-stage upgrade while retaining the factory source unit using a PAC Audio line-out converter.

Amplifiers will come with RCA’s inputs, sometimes referred to as pre-in’s, “Line Level” or “Low-Level” inputs, that allow the audio signal of a volume controlled source unit to be introduced to the amplification process. Many aftermarket source units, if not all, will come with RCA outputs (pre-out’s) on the rear to pass the audio signal to an aftermarket amplifier. Some stereos will have only a single set of left and right pre-out’s, while most decent to high-end stereos will have at least 3 sets of left and right pre-out’s. The 3 sets of pre-out’s are often dedicated to front speaker, rear speaker and subwoofer stereo signals.

The AudioControl amplifiers are a great example of efficient built-in line-out converters.

Most factory stereos (excluding a run of Toyota/Scion stereos in the mid to late 00’s) do not come with RCA level pre-outs on the back for and easy audio upgrade. If the vehicle you are looking to add aftermarket amplifiers does not have RCA outputs, chances are you will need a line-out converter. As stated above, it is possible to go the route of utilizing and amplifier with built in speaker level inputs, but signal quality could suffer. Taking this route, if the factory stereo is too powerful or has an amplifier that is too powerful, this could in-turn harm the aftermarket amplifiers. Many aftermarket amplifiers will have issues when seeing more than 9-16 Volts of signal input. Now, let’s cover more details of why a line-out convertor is worth the extra bit of money in the audio budget…

What is a Line-out Converter?

In short, a Line-out Converter is a device that converts high-level speaker level signal into low-level RCA signal. When choosing a line-out converter, also referred to as “LOC”, it is important to know how many “pre-in’s” are needed to fully populate the amplifiers. This will help to choose the converter with the proper amount of pre-outs to cover the full aftermarket stereo system. There are two specific types of line-out converters; Passive and Active. Passive, purely means the convertor does not need to be powered in order to work, and that it simply a passes signal. An active convertor will not only pass signal but will generally need to be powered in order to give the signal a slight voltage boost, and in some cases provide a “remote turn-on” for the amplifiers.

Here is an example of an adjustable 2-channel passive line-out converter new, and installed in a vehicle using proper techniques and tools to find the correct factory signal.

Most powered line-out converters will have a feature called “signal sense” (or some form similar like AudioControl’s “GTO Signal Sensing) that is designed to supply 12V switch to the remote turn-on output when the unit senses a signal passing through the wires that have been tapped for source signal. This can then be used as remote turn-on for the aftermarket amplifier. Having a line-out converter that offers the signal sense feature is crucial in the sense that the installation process will be much smoother due to not having to identify a proper accessory wire for the amplifiers remote turn-on. Personally, this has to be one of my all-time favorite features on any device.

Examples of a both a 2-channel and 4-channel PAC Audio integration adjustable active line-out converters.

Some vehicle stereo systems will not work properly if they sense a speaker lead has the improper resistance. This could be due to the omission of the speaker itself, a different voice coil configuration of a new speaker, or the added resistance values of the LOC tapping the signal path. In this scenario it is important use the resistors of the correct values to counter the issue. This is the reason why many factory amplifiers cannot be removed from newer vehicle audio systems, and possible reduced functionality at the source unit. At LIS Audio we will use a combination of an AudioControl Signal Processor along with AudioControl LGD load resisters to prevent issues while adding new amplifiers. We will touch on this a bit more in the next section as we cover signal processors.

An AudioControl LC2i was used in this Ford F-150 to add a couple Massive Audio 6″ subwoofers in a custom enclosure under the rear seat.

When tapping signal from the factory source unit, it is important to know whether there is a factory amplifier in the system and if the line-out converter being used can properly handle the amount of power to be transferred through it. Many line-out converters, especially passive, will not hold up to a powerful signal introduced after the factory amplifier, but rather before where the signal is weaker. Some active LOC’s, like AudioControl products, will handle up to 400 Watts of speaker level input. These factors come into play depending on the vehicle and the extent of the audio system it has from factory. Many audio systems will not allow for signal to be integrated into after the stereo and before the factory amplifier.

An example of a previously improperly installed passive line-out converter that was so over powered it began to overheat and melt the entire device.

Many powered line-out converters will allow for the addition of a model specific bass knob, or controller. Be sure to look for this option when selecting which unit to purchase. For example, the AudioControl LC2i is capable of having a bass knob but is sold separately while the AudioControl LC2iPRO comes with a bass knob. Universal bass knobs are available so, this shouldn’t be a make-or-break feature when looking at line-out convertors. Now, for some information on powered signal processors.

What is a Signal Processor?

A signal processor is really and powered device that intakes audio signal and outputs a usable (often more adjustable than a simple line-out converter) audio signal proper for an aftermarket amplifier. In this section about signal processors, we will go into a few more details as to why it is important to have signal adjustability in some vehicles rather than others. Many base model vehicles on the road today will have simple speaker arrangements like so; front component, rear coaxial and possibly factory subwoofer. Most of which can be addressed with passive crossovers and with only 1 or 2 amplifiers. Vehicles with premium sound systems, or that maybe considered luxury, may have upwards to 12 or more speakers spread throughout the cabin and trunk/hatch areas. Each speaker in a premium audio system may also need to receive a dedicated frequency range, as opposed to a full-range signal.

To integrate into the Logic7 factory audio system in this 2008 BMW X5 and add an aftermarket subwoofer, it was crucial that we used an AudioControl LC7i signal processor.

When a vehicle has a factory amplifier that powers each speaker on it’s own individual channel, then the channels are maybe separated into different frequencies. If the vehicle has 3 speakers in the front, on each side of the sound-stage, then they are likely; tweeter, mid-range, and mid-bass speakers. This is a very common configuration in higher end car audio systems and from the factory could have the dedicated signals sent to each speaker. Less commonly, the speaker in the mid-bass position could be a subwoofer. The tweeters would receive high frequencies, while the mid-range speakers would get mid-range frequencies, and the mid-bass speakers would obviously take a mid-bass signal. If the subwoofer is in the back, it would receive the bass the mid-bass speakers are not able to efficiently play.

In order to properly integrate into the factory Sony audio system in this Ford F-150, we used an AudioControl LC7i, which did the job perfectly. Visit our LIS Audio blog ’15 Ford F-150 Stereo System Upgrade to see more on this installation.

The setup described above, is often referred to as “active.” If we were to add a 6-channel amplifier to a VW Jetta and run the front speakers fully active, it would be nice to have a processor that will separate the individual frequencies to each channel, a processor that will tap into factory signal and, also relay the proper frequencies to our new amplifier. For simple and lower budget active installations at LIS Audio, we may use an AudioControl LC7i due to its ability to keep the signals separate, or to sum separated signals together, depending on what the application calls for. It also allows the ability to pass the separated signal straight through but at a safe input voltage for an aftermarket amplifier.

To add a full aftermarket system to this Ford F-150 we decided to use the AudioControl EQS to retain the factory stereo and SYNC system, while gaining more tuning capability. You can see the full build in the LIS Audio blog, Tim’s Ford F150 Audio Anniversary!

If we want to keep the signals separate yet adjust the frequencies of the channels, many times in pairs, we can us an analog Equalizer. All Equalizer’s on the market will vary in the amount of adjustability they may offer. The key factors to pay attention to here are, if the EQ accepts the factory signal (not RCA inputs, but high level inputs), how much adjustability is needed for the application, and if it offers the proper pre-outs for the amplifier/speaker channel configuration. Where going fully active or staying passive the AudioControl LCQ-1 is a great EQ to start with. If a bit more adjustability and “fine tuned” signal separation is required, or desired, the AudioControl DQ-61 is another great option.

To DSP, or not to DSP…

The next step from here would be to add a Digital Sound Processor to perform the job of and LOC, and to gain even more room for adjustability. With the additions of more frequency bands that can be adjusted, in comparison to most equalizers, many DSP’s can also; adjust crossover points, offer time alignment, adjust the sound-stage depth, adjust the sound-stage height and many more features to fine-tune the entire sound-stage. More advanced equalizers may also offer these features, but they are not extremely common. There are many DSP’s out there to choose from, and it is important to do plenty of research and planning for the requirements of the full system before making a purchase.

A picture of the AudioControl LGD load resistors mentioned previously.

Today, adding a DSP to process the factory stereo signal is almost as easy (for a professional shop) and as inexpensive, as adding a line-out convertor, though it do require a bit more tuning. Some DSP’s will offer 6-channels of output, which can easily cover; front speakers, rear speakers, and subwoofer. Others will offer up to, and possibly more than, 12-channels of outputs. It is OK to assume that generally the more channels of output and the more adjustability offered, the higher the price tag. This is why it is important to know not only how many speakers may need to be amplified, but whether the amplifiers versatility will be sufficient enough to skip on some of the adjustability of the DSP to be selected.

This Lexus audio system is a great example of why it is crucial to have a DSP when running many different sized speakers on the front-stage.

Here is an example… Say a vehicle has a 13-speaker system, including two subwoofers under the front seats. The driver wants to amplify the front doors speakers, rear door speakers, and subwoofers. They decide to leave the remaining center channel speaker to be powered by the factory system. The front and rear doors both have component speakers, which will be filtered through a passive crossover for stage separation. It is decided that a 6-channel amplifier and 2-channel amplifier will cover the entire system to be amplified using a 6-channel output DSP. For this we must choose a 6-channel amplifier that has a switch to mirror (or sum) 4-channels together, making it is possible to run the front door, rear door, and rear deck speaker channels, while only having 4 dedicated channels of input. The last 2 DSP outputs will go to our 2-channel subwoofer amplifier.

We added a 10-channel fully active aftermarket audio system to this 2010 VW Passat while keeping the factory source unit by using an AudioControl DM810 DSP. Check out the full build at ’10 VW Passat 2nd, 2nd Amendment Signature Build.

This is one of many examples why it is important to know the equipment that will be purchased and to do plenty of research into the vehicle factory audio signal. Some vehicles will require the audio signal to be up-mixed in order to restore some of the frequencies that have been purposely filtered out, so that the DSP may be fully utilized when tuning. Other vehicles may have an optical or coaxial digital output, which may make integrating the right DSP a dream, just as integrating the wrong DSP could be a nightmare with these inputs. This is when it would be good to use an AudioControl DM608 or DM810, as they offer the inputs needed just for these situations.

This Nissan Armada went from a 4-channel passive audio system, with some installation hiccups, to a fully active 8-channel audio system. An Alpine DSP was used here to retain the factory source unit.

It is also important to know whether there are any other factory sounds or features that may affect the audio signal, such as; fake engine noise, acceleration noise cancellation, or notification chimes. Much of this may be best left to a reputable professional audio shop that has the proper tools and outlets to find the correct information needed. This blog is to merely help educate you on the in’s and out’s of choosing a signal processor that may fit your application, not to cover all the details of properly installing, signal testing, promote the different types of processors, or tuning the system. We currently have, and will have other blogs in the future, on the details of these subjects. Now, let’s wrap it all up!

In Conclusion…

To recap, it is best to know exactly how your factory audio system is setup, and then start to discern which line-out convertor or processor will work best for the application. Not every vehicle will have an option for integration readily available. Especially when a new model year has just been released to the market. We have also gathered that replacing speakers in older vehicles can also be much easier than newer vehicles on the road. If you would like to know more about replacing vehicles speakers using the proper material and procedures, check out our blogs Speaker Rings & Speaker Install.

These example photos show the results of the AudioControl DM-RTA (Real Time Analyzer) through the tuning process in Toyota Tacoma installation we performed. The full build can be found at Benefits Of An Upgraded Audio System!

The tuning process can be equally as important as the initial planning process. I highly recommend thoroughly reading all installation manuals that come with your new products, front to back. Many of the answers you may seek will be in the manual, which can also typically be found on the product website. Improper tuning can make or break the aftermarket stereo system, which is why it is important to do plenty of research on tuning before attempting, or better yet, ask a professional to help you out. There are also some businesses that will help you tune remotely. You may also attempt to contact the company you purchased the DSP or processor from to ask how to properly set it up.

A few very basic tools used for finding the proper audio signal, checking speaker polarity and efficiently tuning the full aftermarket audio system.

The main purpose of this article is to help prevent those who are somewhat new to car audio from ruining new product, or harming the vehicles components, while attempting to upgrade the stereo system. Understanding the details of this article may also help in saving effort and money in the case of accidentally purchasing the wrong product for the application. If you get to a point in the planning or installation process where you seemed a bit stumped or confused, I highly recommend seeking out the advice of a professional before moving forward. Thanks for taking the time to read this article and I hope it helps with your stereo system planning process!

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