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Trinnov ST2 Pro

Speaker & Room Correction System
By Phil Ward

Trinnov ST2 Pro

Is Trinnov's powerful hardware system the last word in monitor correction?

Regular readers may recall that I wrote about Sonarworks' Reference 4 room and monitor optimisation package back in SOS October 2018 (https://sosm.ag/sonarworks-reference4-studio). At first sight, the subject of this review — the Trinnov ST2 Pro — appears to fall into a similar product category, but it's actually a very different beast. I'll get into the detail of the ST2 Pro below, but first a few discursive paragraphs describing and explaining the problem that Trinnov and Sonarworks (and IK Multimedia's ARC and proprietary systems such as Genelec's GLM) aim to solve would probably be helpful.

Changing Rooms?

Although I wrote 'problem' in the singular in the last paragraph, there are actually two fundamental problems that arise with monitors and their use in enclosed spaces such as studio rooms. The first is the monitor itself — very few of them have anything like a flat amplitude or phase response. We're used to seeing specifications of purely electronic audio hardware that describe the frequency response as being flat to within perhaps ±0.1dB and a phase response (put somewhat simplistically, phase can be imagined as frequency-dependent latency; see box) that varies hardly at all. But monitors are very different: a ±3dB window on pass-band amplitude response measured at a single far-field position in space is considered acceptable, even before factoring in that the response is likely to be very different at a relatively nearby measuring position. And a monitor's phase response typically changes by many tens of degrees through the audio frequency band and, again, is very unlikely to be consistent at different measuring positions. A monitor specification I read recently described low-frequency latency of 35ms at 50Hz — that implies a phase change, referenced to zero latency, of 630 degrees.

Put simply, the results of these monitor time- and amplitude-domain errors are that: the frequency balance of programme material will be distorted, and the arrival times of different elements of the programme material will be skewed. Analysing the audibility of such errors is anything but simple, and depends on numerous factors in addition to their fundamental severity, and countless academic studies, technical papers and heavyweight texts have been published on the subject. The complexity of such analysis arises because once we move from the objective realm to the subjective, our brains become involved — and we enter the world of psychoacoustics. Not only is psychoacoustics a fiendishly complex field of study, but every brain is different (and changes all the time), so there's not even such a thing as a fixed reference. Brains are also almost magically adept at error correction, information gap filling and noise reduction. Of course, we have no conscious concept of our brains working near miracles to make sense of audio stimuli, but that's undoubtedly what's happening under the hood... or, perhaps, hat.

The second fundamental problem is the listening room. Not only do monitors mangle the time and frequency elements of audio programme material to an extent that would be laughably unacceptable if found in, for example, a microphone preamplifier, but the listening room has its own go at mangling things too. Wherever we're listening, even in the best-sorted room and even with the flattest monitors, our ears (and brain) are continuously bombarded by audio that's been reflected, perhaps multiple times, from the walls, floor, ceiling, items of furniture, and even other people. And each one of those reflections will not only be imprinted with the specific frequency and phase response of the monitors at the angle in space that created the reflective path, but each reflection will skew the audio still further. It gets worse because listening-room acoustics are not entirely passive. Particularly at low frequencies, standing-wave resonances (where the distance between reflective surfaces is mathematically related to the wavelength) can add significant narrow-band gain — 10dB or more is pretty normal — and for every room resonant peak there's likely to be a related suck-out.

Considered objectively, it's always seemed miraculous to me that monitoring works at all. Again, it does so because our brains have evolved such immensely powerful tools dedicated to processing and making sense of audio stimuli. And that's where Trinnov and their ST2 Pro step in — this device aims to correct some of the phase and amplitude response errors of monitors and rooms and, along with giving our poor, overworked brains an easier ride when they're trying to make sense of audio, to create a more consistent,...

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Published July 2019