DSP – Vital For Great Quality Car Audio Upgrades

DSP – Vital For Great Quality Car Audio Upgrades


 

There are an increasing number of Digital Signal Processors (DSP) on the market these days. It would be a mistake to think of signal processing as a new thing however, and an even bigger one to think of DSP as a need created by product development and marketing  departments within huge multi national conglomerates.

On the face of it though, these innocuous black boxes often buried deep in the bowel of an upgraded car are, at best ignored and at worst seen as an unnecessary expense by casual commentators. This is actually the opposite of our view of these miracles of modern digital technology. It is due to the rise of the DSP that cars are able to sound so good – they can also dramatically cut the cost of a great car audio install.

How so? Car audio is beset with physical barriers to great sound. The major one of these is speaker placement. I have never been to a cinema/theatre or a concert venue where the speakers are mounted at my feet pointing across the stage towards one another or where tweeters, midrange and woofers are separated by vast distances. The reasons for this in such environments are blindingly obvious. In the home, speakers are elevated and face toward the listener. Many high end home hifi speakers use coaxial midrange and tweeters in order to deliver a conjoined listening experience. With low bass and particularly sub bass, some separation can exist as our ears are not good at discerning the source of such frequencies however, this can lead to the need for some phase adjustment to keep bass in perfect synchronisation with directional frequencies. Up until now, installers seeking audiophile quality in a car or even just a well defined sound stage were faced with having to physically move speakers to accommodate this. Imagine the work that goes into lifting 3″ mid range speakers to near ear height. What do you do with the vacant factory positions? How do you return a vehicle to stock condition? how do you hide the fact that you have upgraded your sound for on-the-road sanity without your boss or lease company finding out? The final consideration here is the cost of carrying out the work. DSP starting to look like a cost effective solution now? – Good.

Woofers to the toes, tweeters to the elbows!

So, how is it possible to fool your ears into thinking that your speakers have been moved and establish a solid sound stage with both width and depth? – I am no expert on psycho acoustics but I do know that the brain is very sophisticated when it comes to sound and fooling it is not easy. The first element is time alignment. A decent processor, like the one pictured above is able to delay signals from one or more speakers (whether that be woofer, mid range or tweeter), so that sound reaches both ears at exactly the right time. Traditionally, the time delays required are calculated by first measuring the distance from speaker to ear and performing calculus based on the speed of sound through free air. We are talking about delays of very small amounts. For instance, sound takes 14.6 milliseconds (thousandths of a second) to travel five meters. So, a processor needs to provide extremely fine adjustment of time delays and for this it needs processing power akin to that in a good laptop or desk top computer. It is also preferable to have a good pair of ears behind the controls! Alternatively, Audison bit processors can be tuned by machine (Audison bit Tune). This takes the human element away and having had this done to my own car, I can vouch totally for its efficacy when it comes to time alignment! – Be aware that as with every great product, there are some not so good products which claim to do similar things but are built to price rather than precision!

Once time alignment has been undertaken, the DSP can then be set to work on dividing the frequency spectrum up between however many speakers are used. Once more this can be done by ear or by bit Tune in the case of Audison bit processors. Here things become a little less scientific and a nod needs to be given to the personal preference of the end user. Yes, an automatic set up can get you to a decent starting point but, depending on the sophistication of the device employed, a lot more can be squeezed out of the speakers using a good pair of ears. Unlike passive crossover networks, which tend to work on a set frequency with perhaps a 2dB attenuation switch, a DSP is capable of almost infinitely fine adjustments. Equalisation can also have a dramatic effect on sound stage, particularly in a car where as previously mentioned, speakers can be mounted significant distances apart. As with all things audio, the final setting is a compromise between achieving perfect sound stage and providing a warm, musical reproduction faithful to an original recording. Always remember the primary purpose of DSP in a car is to reproduce an original recording as faithfully as possible, not just to change how it sounds!

Having experienced many varieties of signal processing in many vehicle’s, I have to add a gentle warning. Good DSP’s offering fine adjustment can actually save you money. However, there are many head units on the market which contain rough and ready adjustment which in my opinion, are not engineered well enough to achieve what is needed and will result in frustration. As always, I would always recommend you put yourselves in the hands of your local FOUR MASTER who will have experience of working with DSP’s on a daily basis and will be able to point you in the right direction.

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