||THX Optimode Audio Calibration
The Trials and Tribulations...
By Stuart M. Robinson.
Please note that the following article applies to THX Optimode only, it is not to be confused with LucasFilm's updated and corrected system calibration material, now re-badged as THX Optimizer.
THX Optimode, developed by the THX Digital Mastering Program (the same folk who are responsible for THX software) was introduced on June 6th 2000 with the region 1 DVD release 'Fight Club'. The DVDs pictured along the right-hand side of this article all contain THX Optimode signals (click upon one to learn more), and you can view a complete list on the final page.
While the Optimode video test material provides a valid method of evaluating your display device, the audio calibration signals have been a source of much confusion.
To be fair to THX, they have recently stated that the Optimode calibration noise should not be used to assess the output levels of a system, although this advice does contradict the original Optimode press release which reads: THX Optimode provides tests for speaker level, speaker phase and Low Frequency Effects (LFE) channel crossover.
The reason for THX's change of heart is clear from the results of my own investigations. The THX Optimode calibration noise is inaccurate, in some cases by as much as 10dB.
To understand why, we must concentrate on the volume levels at which calibration material is produced, an area of decoder/receiver operation and instructions passed to decoding hardware by the Dolby Digital bitstream itself.