Input Level Calibration

have a poorly-defined image smeared all over their end of the room.

•L–C Phasing: check Left-Center phasing in the Home THX mode by repeating the L-R Phasing test after having moved the intercon- nect from the Right speaker’s amplifier input to the Center speaker’s amplifier input. Don’t forget to move the interconnecting cables back where they belong when you are done.

•Absolute Subwoofer Phasing: it is also important for both sub- woofers to have the correct phase with regard to the rest of the system. Now that the LCR speakers are all matched, play the 80 Hz warble tone from the Stereophile Test CD. Alternatively, listen for the “body hits” (when Indy gets slugged) in WOW! (These body hits have a lot of energy at approximately 80 Hz.) Reverse the polarity of all subwoofers (if using more than one) and listen again. The polarity with the greatest bass output in this vital region is correct.

•Surround Phasing: using the pro logic mode (not the THX cinema mode), stand halfway between and at some distance from the sur- round speakers with them facing you. With strong surround pro- gram material (such as Chapter 11 on WOW!, or the out-of-phase pink noise test on the Stereophile Test CD), you should hear a solid center image hanging between the surround speakers. (“Absolute” phasing of the surrounds with regard to the front speakers is rela- tively unimportant, since the delay used to take advantage of the precedence effect destroys any front-to-back phase integrity.)

A few minutes of extra attention paid to phasing at this stage of the installation pays off handsomely in improved localization and in optimal bass performance. This is particularly true if the amplifiers used are not identical.

It is necessary to adjust the input level of sources in order to get the best results from the system when used in either THX cinema or pro logic modes. This is be- cause Dolby Pro Logic employs a modified version of Dolby B noise reduction, which needs to be calibrated in order to ensure accurate tracking and decoding of the soundtrack. This adjustment yields the best dynamic range from the sur- round decoder circuitry, and ensures accurate tracking of the steering circuitry in Dolby Pro Logic. While not hyper-critical in the PAV, thanks to its extraordinary signal-to-noise and headroom performance, adjusting it accurately will squeeze the last bit of performance from your system.

A simple test tone can be used in conjunction with the front-panel level indicator to calibrate the system. (Ch. 5 on Lucasfilm’s WOW! test laserdisc, or a copy thereof for your VCR; Track 1 of the first Stereophile Test CD also has a suitable - 20 dBFS, 1 kHz test tone.) Lower the master volume to “background” music levels and then turn on the test tone. Adjust the input level until until the green LED just above the input level button just turns on.

If no test tone is available, you can still calibrate the system with reasonable accu- racy by turning up the input level control until the green LED is on most of the time during loud passages in movies, but so as to prevent it from turning red at any time (which would indicate the onset of clipping in the Dolby Pro Logic cir- cuitry). Various movies are dubbed at slightly different levels, so you may want to touch up this adjustment occasionally. Expect to see a 1-3 dB variation among various film transfers.

Default input level settings may be set for each input in the PAV. Setting these de- faults for each source in the system will have the effect of transparently eliminat-