I suspect that every immersive audio fan has their own personal wishlist of albums they’d like to see adapted to a multichannel format like 5.1 or Dolby Atmos. In place of a true immersive remix from a multi-tracked source, the next-best option is to purchase Involve Audio’s Surround Master. Not only does this unit effectively convert stereo into a convincing quasi-surround sound, but it will also handle playback of vintage quadraphonic vinyl recordings from over four decades ago.

In the early 1970s, when the music industry began a short-lived experiment of remixing popular albums in quadraphonic sound (an early form of immersive audio that utilized four full-range speakers arranged in a square formation around the listener), audio engineers and equipment manufacturers were given an impossible problem to solve. Vinyl long-play records, the most popular music format at the time, were incapable of carrying more than two channels of sound. If the new quadraphonic format was to catch on and ultimately supersede stereo as its architects envisioned, it would have to be available on vinyl LP.

A solution to this issue ultimately arrived with the invention of a process known as surround matrix processing. The key concept behind surround matrix technology is the ability to encapsulate four channels of audio inside of a stereo-only medium, such as the vinyl LP, using acoustical phase manipulation.

Studios outfitted for quadraphonic mixing in the 1970s used a matrix encoder (a large piece of outboard gear with four inputs and only two outputs) to collapse the original four channels of audio into two. This new two-channel “encoded” master was used to manufacture quadraphonic LP’s. The consumer would then have to purchase a matrix decoder (a preamp-like device with two inputs and four outputs) to convert the two channels of audio on the LP back into four channels on their home quadraphonic system.

Clever as this process was, it had a critical flaw: imperfect channel separation. Immersive music mixes often feature instruments or voices isolated behind or in front of the listener. The process of playing back a matrixed quadraphonic LP will inevitably alter the positions that the mixer assigned each element that makes up the album.

As an abstract example, let’s say that the quadraphonic remix engineer has decided to pan drums across the front two speakers and place a rhythm guitar in the rear speakers. Due to the limitations of the matrix decoding process, the listener playing back this mix on LP will hear some drum sound in the rear speakers that isn’t supposed to be there at all.

Though poor matrix processing technology contributed to the critical and commercial failure of quadraphonic sound, it also became its most enduring legacy. Quad enthusiasts at the time realized that their matrix decoders would also produce a convincing faux surround effect from standard stereo vinyl.

Equipment manufacturers such as Dolby Laboratories continued to improve on stereo-to-surround processing, or “upmixing” as it is colloquially referred to, over the next several decades. This eventually culminated in the development of a digital upmixer called “Pro-Logic II” that still comes built-in to most audio/video receivers today.

Today, Australia-based Involve Audio has introduced a new standalone matrix decoder called the Surround Master. This review concerns the original “V1” model, which has since been revamped to include a metal case and individual volume controls for each channel.

Billed as “the ultimate system upgrade,” the Surround Master has a number of unique processing capabilities that set it apart from similar products in both hardware and software form. Its main feature is Involve Audio’s proprietary stereo-to-surround upmixing process, but it also supports playback of vintage quadraphonic LPs encoded in the Columbia “SQ” matrix system. This process was used on hundreds of quadraphonic LP’s from the early-to-mid 1970s, making it attractive to longtime quad enthusiasts who no longer have to rely on their decades-old irreplaceable decoding units to experience their vast record collections.

To evaluate the Surround Master’s stereo-to-surround upmixing performance, I played the song “Then Came The Last Days Of May” from the Blue Oyster Cult’s 1972 self-titled debut album (KC-31063). This track demonstrated the decoder’s ability to extract “in-the-room” ambience and delay from the recording and move it to the rear speakers. I was also impressed by how it kept the lead vocal anchored to the front speakers, with very little vocal sound permeating the rears. The processing did “open up” the song to some degree, with some of the wider-panned stereo elements like electric guitar and backing vocals moved further back into the room, but I wouldn’t necessarily mistake it for a genuine multichannel remix.

Finally, to evaluate the unit’s ability to decode vintage CBS “SQ” quadraphonic material, I used the rare 1976 quadraphonic vinyl pressing of Jeff Beck’s Wired album (PCQ-33849). Interestingly enough, Sony Japan actually issued a Hybrid Multichannel SACD (EICP-10004) of this album back in the Fall of 2016 that used a digital transfer of the 1976 quadraphonic mix.

The goal here was to see how closely the LP decoded by the Surround Master would replicate the discrete four-channel master used on the Multichannel SACD. Though certain shortcomings of the matrix encoding process are still evident, the Surround Master was able to closely match the new SACD edition by forcefully steering the rhythm guitar and keyboards into the back corners.

Ultimately, I think it’s fair to say that most immersive audio enthusiasts would be interested in the Surround Master primarily for its ability to effectively process stereo into an often-convincing quasi-surround. In this regard, I feel it is superior to systems embedded in modern AVRs such as Dolby Pro-Logic II and DTS Neo:6. However, its ability to correctly play back vintage quadraphonic LPs is what really makes it a critical and unique component in my stereo system.

Support IAA by purchasing the Involve Audio Surround Master V1!

Author picture
About the Author
Jonathan is an audio engineering enthusiast from New York with a passion for immersive audio, having amassed a formidable collection of multichannel optical discs and quadraphonic vinyl. He earned his undergraduate degree in Television-Radio from Ithaca College and is currently enrolled in a Master’s Program in Audio Technology.