Dolby Virtual Surround Sound Technology
A Guide to Dolby Headphone and Dolby Virtual Speaker
Surround Sound Technology
Virtual Surround Sound technology makes it possible to enjoy a 5.1-channel Dolby surround sound through a pair of headphones, or even a single speaker bar playback set-up - also referred to as a sound bar or speaker bar system.
Many may wonder how it is possible to pack five speakers and a subwoofer into a pair of headphones, least image into a single-speaker system! Yet, this is all possible thanks to Dolby Headphone and Dolby Virtual Speaker technologies.
In this article, we discuss virtual surround sound technologies - explaining the principles in the setup of a virtual soundfield around the listener while pointing out the limitations of such systems with respect to a multi-channel speaker setup.
Polk Audio SurroundBar IHT 6000
A compact yet powerful speaker bar system using Polk's proprietary SDA (Stereo Dimensional Array) technology to simulate the immersive soundfield without surrounding yourself with speakers; the included wireless subwoofer helps deliver good bass response that makes sound feel richer.
Available from amazon.com
Introducing Virtual Surround Sound
A virtual immersive sound-field but... to what extent?
It may sound somewhat contradictory - playing a 5.1-channel sound system over an ordinary pair of stereo headphones while still enjoying practically the same immersive experience generated by a multi-speaker surround sound playback system.
Yet, when you start thinking about it, there is nothing contradictory in the whole idea; after all we only have two ears through which we capture all sound information, irrespective of the number of different sound sources present at any time.
In simple terms, this is the concept behind Dolby Headphone Technology. In other words, getting a surround soundstage through a pair of stereo headphones should not be something unrealistic!
But what about Dolby Virtual Speaker technology that enables you to enjoy 5.1 Dolby surround sound listening experience over a single speaker system, more specifically referred to as a speaker bar or sound bar solution? These single speaker surround sound systems use advanced virtual surround technologies that manipulate audio signals with sonic spatial cues by applying varying delays and phase-shifts between the different channels in a 5.1 sound source. The whole process is based on extensive room-modeling technologies to reproduce the sonic spectrum and dynamics of a properly placed 5.1 multi-speaker system in a typical room environment.
Dolby Surround Virtual Speaker technology is just one of the many proprietary advanced digital processing algorithms in use today for single-speaker virtual surround. For example, the Polk Audio surroundbar featured above makes use of Polk's proprietary Stereo Dimensional Array (SDA) technology to simulate the surround soundfield.
Worth taking note here that independent of the digital signal processing (DSP) algorithm used to generate a virtual surround soundstage, these single speaker systems consist in reality of a speaker bar - hence the name sound bar or surround bar - with multiple mini-speakers mounted onto the speaker unit.
A minimum of two such speaker channels are necessary; in fact, to be more precise, both Dolby Virtual Speaker technology and Polk's stereo dimensional array technology are 5.1 virtual surround technologies over a 2-speaker playback setup.
It is through the use of these mini-speakers within the single speaker bar unit that it is possible to generate a virtual surround sound stage. More complex single speaker designs incorporate additional mini-speaker drivers and tweeters - all mounted into the same single speaker unit, while some units also include a woofer driver for improved low frequency response.
Polk Audio PSWi225
A 100W RMS powered subwoofer coupled with the convince of wireless audio connectivity. A more powerful wireless version is also available; it is the Polk Audio DSW PRO 550WI with a 200W cont, rating.
Available from amazon.com
Irrespective of whether a single-speaker bar includes a woofer driver or not, it is best to complement single-speaker surround sound systems with a compact powered subwoofer as in general, bass response of speaker bar systems is quite lacking.
A possible inexpensive wireless subwoofer option is the Polk Audio PSWi225 wireless subwoofer shown here. Despite its compact 1 cu. ft design and 100W continuous power rating, the Polk PSWi225 is capable of delivering exceptionally deep bass performance no sound bar speaker system alone can ever achieve; it dramatically improves the overall audio performance while providing the added convenience of wireless connectivity.
Sound Projection Technology and Virtual Surround
While the majority of single speaker systems rely solely on virtual surround sound digital signal processing algorithms to generate an immersive sound field, others like the 120W Yamaha YSP-4100BL Digital Sound Projector use sound projection technology to create the virtual surround sound stage by reflecting sound off of the room's sides and rear walls.
These systems make use of a large number of micro-speaker drivers to project the sound onto the room walls. The Yamaha YSP-4100BL referred to above uses as much as 40x1.5" micro speakers (or beam drivers) in addition to a pair of 4.5-inch sub-woofers, positioned in such a manner within the speaker bar to literally project the sound and bounce it off the walls to generate a virtual surround soundstage.
Under the ideal room environment, virtual surround sound projector single speaker systems are capable of a good 'convincing' immersive sound stage - with sound that literally feels like coming from behind. They work best with bare walls as these reflect sound better. In addition, for best sound, your seating position should not be located against a wall. Note however that objects in the room such as chairs, drapes, or bulky furniture may interfere with a sound projector effectiveness in generating a truly surround sound field.
For more information on sound bar systems, please refer to our Sound Bar Buying Guide.
Dolby Virtual Surround Sound Technologies - in detail
Dolby Headphone Technology
This allows the listener to enjoy a realistic 5.1 surround soundstage from any pair of headphones when listening to music, watching movies, or playing games, without disturbing others. In other words, it is ideal for personal and portable surround sound listening.
This Dolby Virtual surround sound technology can also be used with 24-bit/96 kHz audio encoded with MLP LosslessTM found on DVD-Audio discs. This means that Dolby headphone technology has the ability to play the best quality audio that is bit-for-bit identical to original studio masters.
It is interesting to note that there may appear two Dolby Headphone technology logos - one using Dolby Digital and the other using Dolby Pro Logic II. There is a rather simple explanation behind these different logos.
Dolby Headphone is designed to process a 5.1 signal, and though it can be used to process stereo sources to get a virtual 5.1 surround sound experience through over an ordinary pair of headphones, the stereo signal must first be converted to a 5.1 signal. Products featuring this form of Dolby surround sound expansion are labeled with a Dolby Pro Logic II/Dolby Headphone logo.
Products with a Dolby Digital/Dolby Headphone logo decode 5.1-channel Dolby Digital soundtracks. In other words, Dolby Headphone processing is applied to the multiple (discrete) channels of an already encoded 5.1 Dolby Digital material to produce the virtual surround soundstage over a pair of headphones.
One major benefit of Dolby Headphone technology is that of improving the listening comfort by reducing what is referred to as 'listener fatigue.' The latter is the result of a rather unnatural in-the-head sound effect produced by standard stereo headphones.
Instead, the virtual surround soundstage produced by Dolby Headphone technology leads to a more natural 'out-of-head' effect that allows the listener to fully enjoy a three-dimensional soundstage that is much easier on the mind.
Dolby Virtual Speaker
Dolby Virtual Speaker delivers a 5.1-channel surround sound listening experience from just two speakers, making it an ideal technology for digital TVs, stereo mini-systems, PCs, and a variety of consumer audio/visual products.
Dolby Virtual Speaker technology also helps create a wider two-channel environment during playback of stereo CDs and MP3s, and when combined with Dolby Pro Logic® II processing, it will deliver a virtual surround listening experience from any high-quality stereo source. The result in the latter case is more than just a simple 'expanded stereo' performance.
Dolby Virtual Speaker incorporates highly advanced algorithms and extensive room-modeling technologies to reproduce the sonic spectrum and dynamics of a properly placed 5.1-speaker system in a typical room environment. This is possible by reproducing the direct and indirect (reflected) sounds as these would arrive at the ear in a real 5.1 multi-speaker setup. This means that this virtual speaker technology has to take into account the lower levels of indirect sound as well as the different spectral balance between direct and indirect sound waves arriving at the ear.
One may say that Dolby Virtual speaker is basically the same as Dolby Headphone. True that the virtual surround sound stage produced in either case is basically the same, but there is a major technological difference between the two.
While with headphone listening, the sound produced by each earpiece is only heard by the respective ear, this is not the case with speaker listening. To create a virtual surround sound stage over two speakers requires not only recreating the sonic signatures for each ear, but also ensuring that neither ear hears the signature intended for the other. In other words, the left ear must hear only the Left speaker, and the right ear must hear only the Right speaker.
Dolby Virtual Speaker technology accomplished this through a crosstalk cancellation technique whereby a delayed mirror image say from the Right speaker's sound is generated by the Left speaker such that when this reaches the left ear, it cancels out the sound arriving from the Right speaker at the left ear. In this manner, the right ear hears sound only from the Right speaker and similarly for the left ear.
To experience the full effectiveness of this cancellation, the listener needs to be in a listening zone equidistant from each speaker.
This renders the listening area somewhat restricted, and therefore, this virtual surround sound technology is most appropriate for such activities as using a PC or casual TV viewing - where a full surround system might be unsuitable or impractical.
The rather restricted sweet listening spot supported by virtual surround sound systems further explains why these systems are most suitable for the small room environment.
Dolby Virtual Speaker technology does provide two listening modes that produce different listening environments. Both differ in the surround effect as well as in the apparent localization of the virtual speakers; these are termed 'Reference', and 'Wide'.
The Reference mode creates a realistic five-speaker surround sound from two speakers with the apparent width of the sound across the front image defined by the distance between the two speakers. Instead, the Wide mode creates a more spacious front image than that defined by physical position of the two speakers used in the playback setup.
Virtual Surround Sound Technology: Limitations worth knowing about
Virtual surround technologies produce more than just an expansive soundfield, and as further detailed above, they also come with a few added benefits - apart from making it possible to enjoy 5.1 surround sound in small rooms without being surrounded with speakers.
1] Keep in mind that the expansive soundfield produced by speaker bar systems is limited to a rather restricted sweet spot; move further away from that sweet spot and the soundfield would soon become unrealistic.
2] Do not expect to enjoy a room shaking bass experience with speaker bar systems unless you add a separate subwoofer unit.
3] No matter how expansive the sound stage is, the performance of virtual surround sound systems comes nowhere close to that of a true multi-channel surround sound speaker setup. In other words, they provide the convenience of zero speaker clutter at the expense of audio performance.
Buying Options for Sound Bar Speaker Systems
Amazon.com offers a complete range of single speaker sound bar systems, often at reduced prices.