decafcappucino,
I'm not sure what you're driving at.....
We have a tuning cd with different tracks recorded at 0dB, -5dB, -10dB, -15dB. Each of these are at 40 Hz, 1 Kz and 4Kz. This is used to set the gain structure of any audio system. We have been dicussing gain overlap.
Gain overlap is a compensation mechanism to account for the fact that we don’t listen to test tones in mobile audio
systems, rather we listen to music. Test tones are great for setting up the input levels on each component of the signal
chain, but test tones are constant levels all of the time. Music has levels that simply are not constant all of the time.
There are loud passages and soft passages in music, and these are constantly changing. Due to this fact, the maximum
unclipped output levels determined by test tones will seem as if the system doesn’t play very loud. Certainly it’s free of
clipping and audible distortion, but it’s not as loud as it seems like it could be overall. This process allows a measured
amount of increase to be implemented without “guessing” by just turning up the gain controls on a random piece of
equipment. Adding extra gain to the signal chain whether it’s at an upstream signal processor or at the amplifier at this
point is a trade-off of benefits and drawbacks. Most people find that there is a good compromise of these trade-offs.
• When you raise the gain above the levels achieved with a test tone, you will lower the signal to noise ratio of the
system. In this scenario, the trade-off is higher output at maximum levels trading off for more hiss and system noise
with the volume at lower levels. There is always an acceptable compromise.
• Additionally, when you raise the gain above the levels achieved with a test tone, you will increase audible
distortion of the system. In this scenario, the trade-off is higher output at maximum levels trading off for more
frequent moments of “clipping” with both the volume and the music at their maximum levels. Check out the amount
of time that there is added distortion in the signal based on the amount of gain overlap added. Once again, there is
always an acceptable compromise.
• Add in 5dB of gain overlap to achieve a higher volume with music (rather than test tones). It’s a safe compromise
between slightly increased distortion (Less than 0.1%) and louder output (nearly 5dB). Less critical listeners could
tolerate 10dB of gain overlap, but look what happens to the distortion increase. Some people will easily hear that with
a great set of mid and high frequency speakers (certainly more evident on compressed audio tracks as well). Reserve
15dB of gain overlap for subs, if at all. If you are using this setting, chances are you can go to a bigger amp for better
sounding results at the same volume levels with less distortion and more headroom.
• Use the gain overlap tracks on the RTTI/3Sixty set up disc to achieve the gain overlap safely without causing damage to
the speakers. Simply play the same frequency (HP/BP/LP) as before and increase the voltage levels to the same place
the recorded measurements were at 0dB levels for 5dB of overlap. If you use the 0dB tracks to increase the output
voltages to do this, you will almost certainly damage the speakers if not using load resistors.
There is a complete tutorial at the top of this section that explains the procedure in more detail.