Ensuring that the output level of your head unit and processors is adjusted in perfect unison with your amplifiers is critical to achieving the best possible performance from your system in terms of signal to noise and system reliability.
To set system pre-amp levels, you will need a CD with known-level test tones that coincide with the frequency ranges your amplifiers will be operating in (in an actively filtered system). We offer the Ultimate SQ Setup CD (USQCD) for just such a task. The CD is available through our Products page, or thought www.genuinecanadianaudio.com. More dealers will be coming online in the next few months.
Setting your gains correctly is a multi-step process, and to do so accurately, will require some equipment. If cost is no object or you own a stereo shop and do this repeated on each vehicle (you do set your customers gains for them, right?) then you need to purchase a high-quality oscilloscope from a company like Tektronix or Kenwood. If you are after something more portable, Fluke has some excellent hand-held units.
If you are on a tighter budget, then you might want to consider a PC-based scope like the ones available from Velleman USA (www.vellemanusa.com). They have some nice units.
If that is still taxing your budget, then one of the Velleman handheld scopes will work fine, and is still a handy unit.
The CD you choose to use will need to contain test tones at different levels to allow you to compensate for CD's that aren't recorded at full volume. If you are competing in IASCA or USACi competition, then achieving a set SPL with your car will determine the settings on your gains. I would use the -3dB tone tracks on the USQCD Disc 2.
Where this becomes tricky is in balancing the effect on any equalization on the system. Remember that every boost of 3dB on an EQ requires double the voltage from the head unit, processor or amplifier. A gain of 6dB means four times the votlage and 18dB, well, if you need that you have a system design flaw.
Turn down all the levels on all the units in your system. If you have an EQ, this should be left equalized to achieve the best overall sound, and if possible, a good sounding curve. Now start by turning your head unit volume up to about 3/4 of full, and listen to the sound. If you can't hear anything, sneak the levels up on everything else a wee bit. Now, turn the head unit up to full. Watch the scope for any clipping or distortion in the output waveform. If you don't see anything, you bought a good head unit and can proceed.
If you do find distortion, go to a track on the CD that eliminates it, or just turn down the volume a notch or two. Once done, go on to the next piece of equipment in the chain. Do this to every piece of equipment in the signal chain and for all frequency ranges. Be sure you use the same relative level on the CD for all the settings (0dB, -1.5dB or -3dB for example) for all frequencies tested.
Once the processors are done being tested, move to the amplifiers. Decide which amp you think will clip first (likely based on your EQ settings) and set it first. You can set it for just the slightest amount of clipping. Set the gains on the other amplifiers in the system to achieve a perfect balance between the frequency ranges.
You will likely need to make one or two tries at doing this the first time, but the results will be impressive in terms of signal to noise ratio, and the lack of speaker failures.
If you make changes to your EQ settings, you will need to redo the gain settings for the equipment down the signal change.
As a final test, use the USQCD Disc 1 and pick whatever frequency is boosted the highest on the EQ. Use the corresponding test tone to ensure you don't have any clipping in the signal path.
Enjoy your system!