Dueling Loudness Corrections Explained
While reviewing the Onkyo TX-SR806 receiver ($1099) I did some to-ing and fro-ing with the THX and Audyssey people regarding THX Loudness Plus and Audyssey Dynamic EQ. These new loudness corrections operate in roughly the same territory--but in a different manner. Their common goal is to compensate for sonic losses that occur naturally at lower volume levels. As volume drops, the frequency response of human hearing changes. Loudness Plus and Dynamic EQ both tackle this problem by adjusting channel levels and frequency response. But beyond that, there are differences between them, and I asked the THX and Audyssey people to be specific about those differences. Here's what they said.
THX Loudness Plus
THX Loudness Plus is part of the new THX Ultra2Plus and THX Select2Plus specs. The following explanation is from Brian Schmidt, Consumer Applications Manager at THX:
The THX and Audyssey descriptions sound familiar because they both address the same basic problems that arise from listening at lower levels than where the content was mixed. They both operate on frequency response and surround levels, so it is difficult to distinguish the technical descriptions. Areas of distinction:
MF: I'm looking at the description of Loudness Plus on the THX site. It seems vague except when it says "THX Loudness Plus automatically adjusts the front-to-back speaker level relationship as you turn the volume level down." The sound waves in the illustration seem to indicate lower volume in the front, and the same volume--but with marginally different propagation patterns--in the rear. Wouldn't this just make the rear speakers sound louder?
Yes, the rear speakers will sound louder when the volume is lowered below reference level. However, this level change is mirroring the perceived level in the mastering environment. We're not just tweaking levels to make it sound better.
The goal of Loudness Plus is to make playback at lower levels deliver the same sense of envelopment as you would get at the higher levels where the content was mixed. The ambient sounds that provide that sense of space quickly become masked and are lost when the volume is lowered, so we compensate for that. It's important to note that when listening at reference level ('0' on the Onkyo AVR), Loudness Plus doesn't process anything. So, it won't make the rear speakers sound louder when used at reference level.
As the master volume is turned down, we gradually adjust the levels of the surround speakers up. This will make the rear speakers sound louder when compared to playback without Loudness Plus, but this is actually much closer to the intended effect that you would get when listening at reference level.
Audyssey Dynamic EQ
Audyssey Dynamic EQ is a feature of some receivers that license Audyssey's MultEQ auto setup and room equalization. The following explanation is from Chris Kyriakakis, founder and chief technical officer of Audyssey Laboratories, and is similar to material on the company's website:
There are several key differences between Dynamic EQ and other methods of loudness control:
Please note that I have not given the THX and Audyssey people a chance to respond to one another. Readers are free to parse their assertions and reach your own conclusions.
If you try the Onkyo receiver, you'll have three options. You can use each feature separately or turn them both off. They will not operate simultaneously.
Note also that they are distinct from other licensed processing used in the Onkyo, such as the THX cinema mode and Audyssey's MultEQ room equalization. Either or both of these can operate with either of the loudness corrections.
Finally, if anyone out there has had a chance to use either THX Loudness Plus or Audyssey Dynamic EQ, please feel free to post your impressions below.