I have written about Loudness Compensation and its importance for home cinema in the context of Yamaha YPAO Volume. If you haven’t checked out that article, I would recommend you do so.
However, I wanted to cover Audyssey’s version of loudness compensation (Dynamic EQ) and dynamic range compression (Dynamic Volume) in this article.
Audyssey Dynamic EQ
Audyssey continued research completed by THX on loudness compensation and did very detailed analysis to come up with updated Fletcher-Munson equal loudness curves.
In summary, loudness compensation compensates for the human auditory system’s perception of sound as the volume is decreased. Firstly, sensitivity to treble and bass seem to drop off as volume is decreased. Secondly, our ability to hear sounds behind us / directionality is decreased with dropping volume as well.
The above of course has critical impacts on playback of multi-channel soundtracks in the home. After all, we rarely if ever listen to movie soundtracks at reference level. That is actually rather uncomfortable in a small space or near-field. So it follows that some kind of compensation is needed if we are to restore the correct perceived tonality and directionality of the soundtrack.
However, Audyssey’s research is unique in that such detailed analysis has not been undertaken by any other company in recent times as far as I know. The result of this research was what Audyssey calls Dynamic EQ.
Dynamic EQ analyses the soundtrack and applies equalisation based on volume level: firstly it lifts treble and bass based on the volume to restore the correct tonality. Secondly, it increases the surround sound field based on volume to restore directionality and surround envelopment.
Audyssey Dynamic Volume
Another issue when listening below reference level in a home cinema is that as we decrease volume, quieter sounds can start dropping below the human hearing threshold – either because of background noise or simply the sounds becoming too faint. After all, movie soundtracks are recorded at a truly massive dynamic range from whispers to a jumbo jet flying overhead. This can result in frustration due to missed dialogue or constantly reaching for the remote due to the soundtrack getting uncomfortably loud.
To compensate for this, we need to apply some kind of dynamic range compression. Audyssey’s solution to this is called Dynamic Volume. What’s great about it is that it works together with Dynamic EQ to restore the correct scale and tonality of each sound as it would be heard in a commercial cinema. After all, sounds that are volume levelled will need different levels of re-equalisation applied.
I would recommend both of these technologies turned on. I always have Dynamic Volume on light / day mode and Dynamic EQ with an offset of -5 regardless of time of day or listening volume. The effect decreases as you increase the volume and switch off completely as you near or hit reference level dependent on the offset chosen.
My view is that house curves – where people start designing a slightly lifted bottom end to the equalisation curve – started appearing because people don’t seem to understand the volume-related tonal shifts due to the human auditory system and the need for a dynamic loudness compensation solution.
The main issue with house curves is that for a house curve to be correct, it would need to be volume dependent – as opposed to it being a fixed curve. After all tonality will shift with volume. Are you going to design a new curve for each 5-10dB difference in the volume?
I only like to advise people to do any sort of house curve with technologies that don’t have loudness compensation functions. For example, DIRAC Live has not yet caught up with Audyssey in this sense and they were using a house curve by default. People seem to prefer it because they haven’t configured their Audyssey receiver correctly. DIRAC Live does have better performance in other aspects, but loudness compensation is not one of them. However, Audyssey can sound incredibly close with the correct setup. Refer to Secrets of Audyssey for more.
Issues with Dynamic EQ and Dynamic Volume
Some users have been complaining that Dynamic EQ and Dynamic Volume are too aggressive making them unusable. Again, I think this is due to setup issues: microphone placement, subwoofer placement or lack of room treatment.
I talk about these issues – and many more – in Secrets of Audyssey which I would recommend to anyone who has not turned on Dynamic EQ and Dynamic Volume or resorted to doing custom curves in the Audyssey app. Unfortunately, neither solution is ideal.