DEQ is not so different from Bass EQ (BEQ) in terms of concept
Let’s dive deeper into the DEQ discussion while we are at it. I’m glad to see more bros here contributing their experience on the use of DEQ along with Audyssey.
If I were to tell you that the underlying objective of DEQ is actually what Bass EQ (BEQ) is trying to achieve all these while? Are you surprise? If we dissect the concepts of DEQ and BEQ, they are probably more similar than you think. While DEQ is a “feature” that works in tandem with Audyssey MultEQ XT32 and BEQ can be implemented using an external DSP like miniDSP to “restore” the SPL of the bass at the modal frequency range - e.g. between 20Hz & 50Hz. I have mentioned umpteen times that the human’s auditory perceptivity of bass in the low-frequency range (usually starts from 50Hz and below) is softer when compared to say a 80Hz tone. According to studies, our hearing is most sensitive in the 2KHz to 4KHz range. The critical spectrum of the frequency range for humans to discern equal loudness be it at the higher end or low end falls somewhere between 500Hz & 5KHz. Any frequency range that falls outside of this critical spectrum will require some kind of compensation to be made - i.e. boost the output (SPL) level in order to achieve the “same” level of output.
According to Audyssey, the “target” Reference curve employed by Audyssey followed loosely to the Harman Curve - in its simplest form, it means a gradual roll-off of high frequency towards the end of the frequency spectrum - usually starting from 4KHz all the way till 22KHz. The drop is gradual from anywhere between -2db from 4KHz onwards till 10KHz and steeper roll-off at -6db from 10KHz to 22KHz. Why Harman Curve and not other target curves? Well, according to Audyssey the roll-off is needed in the higher frequency range to avoid ear fatigue especially from a “brighter” speakers in an untreated room - meaning a lot of sound energy (waves) hitting against hard surfaces which makes listening almost unbearable for movies authored at a higher compression rate.
While we now understand the high spectrum of the frequency range and its implications, let us look at what Audyssey Reference Target Curve does to the lower spectrum of the frequency range - i.e. from 250Hz to 20Hz. This is where the contention comes in. Audyssey without DEQ enabled will strive for a “flat” frequency response. This is the reason why when DEQ is turned off, it attenuates (weakens) the bass, thereby making it “less” boomy. For members who did not follow strictly on ideal speaker/subwoofer placement ritual (like using the Harman Room Mode Calculator) may often find their bass to be muddy and bloated when listening at a reasonable Master Volume (MV) and this can be anywhere between -25db and -10db. The issue with DEQ turned off is that, one will feel the urge to increase the gain on your subwoofer(s) or the trim values in your AVR to compensate for the “loss” in bass output in the lower frequency spectrum. The problem with this method is the need for you to constantly fiddle with the gains/trim levels for different kinds of content being thrown at. With an external DSP like miniDSP, one can implement filters at the key modal frequency and apply a custom “house curve” to compensate for the drop in overall bass output (SPL level). That is the reason I have never ever doubted Roni, Jag and a few other members who used miniDSP to fix some of the “undesirable” effects caused by DEQ.
So what exactly caused DEQ to have some form of undesirable “side-effects” when enabled?! If this is a poorly-implemented feature by Audyssey, why then there is a split of 50-50 amongst members when it comes to DEQ? Another problem associated with DEQ. That is when it boosts the bass output at the lower frequency range, DEQ actually implements this “boost” to other channels as well instead of just the (.1 channel) LFE. Furthermore, Audyssey also implemented their very own Loudness Management algorithm on the surrounds and surround back channels by running it at least 1 - 2db hotter when DEQ is engaged. This is to compensate for the “softer” surround effects when we listen to a lower MV below the Reference level. So DEQ introduced 2 types of boost - i.e. boost in low-frequency range to maintain a bass level that plays at the same output as the rest of the speakers and the other is the boost in surrounds levels. These arbitrary “boosts” created by DEQ makes it harder for us to control IF you did not have an ideal HT setup like the good placement of speakers and subwoofers and proper Audyssey calibration. But I wouldn’t throw in the white towel into the ring just yet. The “workaround” could be found in the Reference Offset Levels (RLO).
But before we dive in on the topic of RLO, it is important to realize that both DEQ and Audyssey worked hand-in-hand to create the Harman Target Curve. Since most of us are now aware that DEQ has to be turned on in order to get back the missing or weaker bass output at the lower frequency range. Now that we have a better idea of how the “full effects” of DEQ can render your HT system to sound worse…we can now touch on the RLO in the next post.