Dirac Modes: Soundstage Control at Your Fingertips
Let’s say you have quite a firm opinion about how you want your music to sound. You want it to sound clean and tonally well balanced with just enough bass—not too much. You want the center image to be right there, dead in the center no matter how you move or where you sit, and you want the sound stage to stay symmetrically within 30 degrees to each side of the center image.
Switch to watching a movie. You want that bass to really deliver the LFE while being able to hear— crisp and clear—what that character is saying in that important dialogue that sets the story for the rest of the movie. And when the action begins you want to feel as if you are there, with the sound effects surrounding you to keep you right in the middle of it.
Now wake up and realize you’re not at home in your sofa with your expensive TV and surround receiver, or your tube amp and stereo speakers. You’re on a train, and the sole provider of this experience is your smartphone.
No, I’m not going to tell you that the sound from your smartphone can be exactly the same as your home cinema—that’s not my point, at least not in this post. My point is that your preference for how the content should sound may change slightly from one use case to another. If you first listen to music and then watch a movie, you want the experience to be slightly different. It’s not about huge, night and day changes—good sound should be good no matter what you listen to. But some small adjustments may be warranted, like adjusting the soundstage, putting some emphasis on the voice, and making the crashes really sound like CRASH!
While this may seem relatively straightforward to achieve, remember that I’m talking about a smartphone here—and not the headphones, but the smartphone’s internal speakers! Also consider that in a case when there are two loudspeakers on a smartphone, they are usually completely different from one another.
So how do we go about achieving something similar to a soundstage in the first place? And, once we have achieved a soundstage, how can we then adjust it from enveloping to frontal?
Let’s begin with the soundstage width
The basic technology used to achieve a soundstage on a smartphone with any width at all is a psycho-acoustic consequence of applying a technology known as crosstalk cancellation. In our high-performing flavor of this technology, we use filters custom designed for the given smartphone speaker configuration. To keep the soundstage coherent and balanced, Dirac has developed a pre-processing module that assigns different parts of the content to different parts of the soundstage. While the full functionality of the module would be far too complex to control for most users, we decided that we wanted to expose one single parameter to control the width of the soundstage. Since there was no single parameter available that would do that, we had to construct it. This is what led us to develop the high level tuning control framework that we call Dirac Modes.
How do Dirac Modes work?
Now I’m not going to tell you how a pair of completely different tiny speakers pointing in completely different directions can be controlled and co-optimized to deliver a realistic and natural soundstage that’s far wider than the physical boundaries of the smartphone. My colleague Jakob Ågren did an excellent job describing the technology behind Dirac Panorama Sound in his blog post. What I am going to explain is how, with Dirac Modes, you can control the soundstage and other high level qualities using nothing more than the tip of your finger.
Basically, Dirac Modes encapsulate the many complex adjustments necessary for achieving a nice sound experience transition from one end of the range of possible settings to the other. In the case of the soundstage, this means making sure it sounds good at all points along the way, from the “very narrow soundstage” to the “very enveloping soundstage.” Dirac’s sound tuning engineers achieve this by working together with each smartphone manufacturer in order to define all the intricate details behind these settings, also ensuring that the sound quality well represents the brand profile of the smartphone.
The Dirac Modes framework is also very flexible
Soundstage width is only one example of a high-level parameter that can be defined and exposed for simple control. Additional parameters can be defined and tested on the fly without the need to develop any new functionality or software. This allows for a high degree of differentiation between different brands and devices. We’ve done some experiments with Tonal Balance using a single parameter to adjust the balance between highs and lows rather than exposing a multi-band graphical equalizer—and it’s even simpler than two knobs marked “bass” and “treble.”
There’s also a parameter for Loudness that—on one end—kicks in when you’ve already cranked up the volume to max but just want to increase it one more notch to overcome the noisy environment and hear what that video blogger is saying. The Loudness parameter will let you prioritize loudness over other qualities such as soundstage width or tonal balance by simply pressing that Volume Up button one more time beyond the normally available range. On the other end, the Loudness parameter lets you play at a low level while enhancing the lows and highs that, due to the human hearing threshold, might otherwise become inaudible.
Another advantage to the flexibility of Dirac Modes is that the parameters do not necessarily need to be exposed for everyone to adjust. Not everybody wants to be bothered with the manual work of adjusting the soundstage from enveloping to narrow. Instead, the smartphone manufacturer can group and hide the different setting possibilities behind a Music Mode or Movie Mode which have both been optimized according to these settings in order to deliver the best experience for their corresponding content types. The switch can be done manually by you, the user of the product, or simply left for some intelligence on the device to decide automatically for you.
With Dirac Modes, smartphone manufacturers don’t have to make the choice between loudness and sound stage when designing a new smartphone—they can have both. Instead, the choice can be left up to the end user who can adjust these qualities to their liking, depending on preference or whatever the current situation calls for. For example, the recently released Xiaomi Mi6 makes use of a Movie mode and a Music mode to enable users to switch between the typical settings that these different usage scenarios require for both headphone and speaker playback.
– Nilo Casimiro Ericsson, Co-Founder and Head of Product Management BU Mobile at Dirac Research