Hear Technologies Hear Back Octo

With the Hear Back Octo, you can add personal foldback mixing functionality to almost any live–sound or studio setup.

Good foldback monitoring — whether in the studio or on stage — is one of the key prerequisites for a good performance, and it generally makes everyone's life a lot easier, quicker and more productive if each performer is able to adjust their own foldback mix to their specific individual requirements.

The latest generation of digital consoles makes that possible by allowing remote control of individual console outputs from a smartphone or tablet, but what about older digital or analogue consoles, where remote control is not an option? In these cases either separate foldback mixes have to be created on the console by the mix (or monitor) engineer, or some kind of ad hoc setup is required involving several local compact mixers each receiving multiple sends from the desk.

However, a more elegant solution is available from American manufacturers Hear Technologies, who make a variety of nicely engineered personal monitoring systems to address precisely these kinds of situations. The most affordable model, introduced in 2018, is called the Hear Back Octo, and it replaces the company's original Hear Back system, which has now been retired. The Octo provides better sound quality and performance than its predecessor, but it remains completely compatible with that original system, so Octo mixer panels can be used to extend an old Hear Back system, or old Hear Back mixer panels can be used to extend a new Octo system, which is useful to know.

On the other hand, while looking superficially similar to the company's impressive flagship foldback system called Hear Back PRO, the Octo system is not interoperable or compatible with it in any way, and damage will occur if elements from these two different systems are interconnected.

Comparing the two systems, the Octo is a scaled-down and more affordable alternative, costing roughly half as much as the equivalent PRO version. Savings come from having only half the distributed channel count (eight mixer panel channels instead of 16), and much simpler input connectivity facilities with no modular options for Dante or Waves SoundGrid interfacing, for example.

Therein Lies The Hub

The system supplied for this review was the Octo Four Pack, which is a complete functioning system aimed at the typical band or small studio. It is supplied with a tough, black, nylon, padded tote bag with internal dividers to store the Hub unit along with four included mixer panels and all the necessary Cat5e connecting cables, an IEC mains cable, an AES59 D-sub to D-sub cable, and a set of mixer overlay cards to mark settings — everything typically required to get up and running quickly and easily. Additional mixer panels can be purchased individually, if required, and the tote bag can house eight individual compartments if the Hub is removed. Other accessory options include cables, stand adaptors, extra overlay cards and so on.

Lying at the heart of the system is the Octo Hub, a 1U rackmounting chassis which accepts the input signals and mains power, and drives up to eight remote mixer panels. The unit is quite shallow, extending just 127mm behind the rack ears, and weighs only 1.8kg. Essentially the audio distribution system operates with a high-speed, eight-channel digital bus called the HearBus, with the input signals routed onto this bus, and the mixer panels picking up the required signals from it. Analogue inputs, and the mixer panel monitor outputs, are handled by 24-bit converters operating at base sample rates (44.1 or 48 kHz), and the system input-output latency is specified as less than 1.5ms — a negligible delay for most applications and almost entirely due to the converters themselves, although I have known a few vocalists who found even that kind of delay objectionable or distracting.

Up to eight mono inputs can be connected at the rear of the Hub, either in digital form via a single ADAT light-pipe port (44.1 or 48 kHz sample rates only, of course), or as balanced line-level analogue via a standard AES59 (Tascam-format) DB25 socket (the maximum analogue input level is +18dBu). Only one input format can be used at a time, selected by a front–panel switch (see below), but adjacent channel pairs can be linked for stereo operation if required on the mixer panels.

The Hub can accommodate eight inputs, via either ADAT or analogue DB25, and distributes those digitally to the artist mixers via Cat5e cables.

The Hub has an internal universal mains power supply which accepts 100-240 V AC from an IEC inlet on the rear panel, but there is no mains on/off switch. The unit consumes a nominal 125W. A pair of RJ45 connectors at the rear provide an input to, and output from, the HearBus, allowing other Hub units to be connected in a daisy-chain fashion to extend the number of artists' mixer panels connected to the system. Hubs can be located up to 160 metres apart. A group of eight more RJ45 sockets provide connections for the remote Octo mixer panels, which can be placed up to 60 metres from the Hub.

Although standard Cat5e cables are employed, the Hub does not operate with standard network data or even conventional PoE supply voltages, so the Hear Back Octo system cannot — indeed, must not — be connected to standard network hubs or switches. However, simple passive point-to-point cabling as part of a building's infrastructure could be used, if appropriate. The connector pin-out and signal details are included in the comprehensive manual, which explains that the bespoke format carries a high-speed multiplexed digital audio signal on the Cat5e cable's first twisted pair, running at 12.28MHz. Reference grounds are carried on the second pair, with a +17.5V power rail on the third pair, and symmetrical ±17.5V power rails on the last. Connections between the Hub and mixer panels are point-to-point only and cannot be split or Y-corded in an effort to run multiple panels from a single outlet.

Sensibly, the individual power supply feeds to each of the eight mixer panel sockets are protected by solid-state resetable fuses, so that if a cable is damaged only that specific outlet is (automatically) isolated, and all the other mixer panels continue to function normally. The fuses reset when the fault is removed.

I mentioned the Hub unit's input source selector earlier, and this is a three-way slide-switch on the front panel which chooses between the ADAT, analogue or HearBus connections as the system's input source. Although only one source can be selected at a time, the others can be left connected if desired, for fast selection between different sources.

There are no other front–panel controls on the Hub, but eight multicolour LEDs indicate the input signal level, and another (Clock) LED illuminates when the HearBus system is operating correctly. The input LEDs change colour with increasing signal level from blue (-32dBu), to green (-10dBu), yellow (+4dBu) and red (+16dBu) — this last being within 2dB of clipping. The Clock light is blue when all is well, and red when not.

Mixer Panels

The artists' mixer panels feature a tough, wipe-clean ABS case with a 5/8-inch threaded insert in the base to allow convenient mounting on a mic stand or bracket. 'Ball and socket' adaptors are available separately to allow the mixer panels to be angled, which is an attractive option. All of the panel connectors are at the front of the unit, protected under a lip, with blanking plugs in the less used sockets, and a channel is cut into the base to grip a standard Cat5e cable, routing it neatly to the rear while also providing welcome strain-relief to maximise the connection's reliability.

The mixer panels each have both eighth- and quarter-inch headphone outputs (wired in parallel), plus stereo line outputs and a stereo mini-jack aux input.

Stereo headphone outputs are provided simultaneously on both standard quarter-inch and eighth-inch jack sockets, wired in parallel. A stereo pair of balanced line outputs are presented on two more quarter-inch TRS sockets, and these can be used to feed a personal in-ear monitoring system or a floor monitor. Usefully, if only the left line output is connected it automatically provides a mono sum of both channels.

An unbalanced auxiliary stereo input is provided on another mini-jack socket, so each artist mixer panel can actually combine 10 inputs. This auxiliary input is intended for an MP3 player, a local click–track source, or a keyboard mixer's output, for example, and as it can accommodate a maximum input level of +22dBu, it's almost impossible to overload it! Rather than provide a separate input level control for the aux input, though, it is assumed the signal level can be controlled directly from the connected replay device itself. The auxiliary input signal is summed with the main stereo mix after the D-A converters and just before the master level control, so it has zero latency.

For the user, the controls comprise just eight rotary channel faders to blend the eight channels sent from the Hub as desired, plus a larger master volume knob to set the required listening or output level. Four concave (capacitive) touch pads activate stereo linking between the corresponding channel pairs if touched for more than one second (blue LEDs above the buttons confirm the linked mode). In normal use, each of the eight mono input channels is routed equally to both the left and right monitoring outputs, but when stereo-linked the odd channels feed just the left output and the even channels the right output, and only the left channels' controls (1, 3, 5 or 7) adjust the mix level for both linked channels. The linking configurations are retained when the unit is powered down.

A status LED at the top of the panel lights blue when the unit is connected to the Hub and receiving valid data and power, but if a headphone fault is detected it flashes blue/red. A second LED near the master volume control also lights red if there's a problem with the headphone amplifier, such as a short-circuit in the output connection, or if the headphone load impedance is too low (16Ω minimum) or the amplifier is overheating. When a fault is detected the amplifier shuts down automatically but returns to normal operation once the fault condition has been resolved.

The eight input channels are mixed in the digital domain and the resulting stereo signal is converted with a Burr Brown PCM1753 stereo delta-sigma D-A converter, which claims a nominal 106dB dynamic range capability. This is not exactly state of the art, but is perfectly acceptable in this application. The headphone amplifiers are based around Burr Brown's chunky OPA551FA high-voltage, high-current op-amps and they are capable of driving headphones with impedances between 32 and 600 Ω — although headphones of less than 150Ω are recommended. Peak power delivery is a substantial 2W with 50Ω headphones, while the balanced line outputs can produce a whopping +28dBu!

The Octo system is quite excellent. It's simple but well specified, very well built, extremely easy to install, it sounds great and has an extraordinary amount of volume.

In Use

Hooking up the Octo is very straightforward. I mostly used it with analogue inputs via the supplied AES59 breakout cable, but I also confirmed it was perfectly happy working with ADAT sources. I couldn't check the HearBus connection as I only had the one Hub unit, but the concept of daisy-chaining multiple Hubs to drive more mixer panels is simple enough.

The Clock LED on the Hub and Status LEDs on the mixer panels all provide confidence that everything is working correctly, and the level indicator LEDs for each channel on the Hub are also reassuring. I found that there is so much gain available from the mixer panel that the actual input levels aren't that critical, and noise really wasn't a problem at all even with pretty low-level analogue inputs. With digital sources, multitrack sources averaging around -20dBFS still produced plenty of headphone level, and material peaking close to 0dBFS was capable of some seriously high levels indeed!

And that's probably the single most important aspect of the Octo system: this thing can go very loud indeed, so some care is advised when plugging headphones in and adjusting levels! I mostly used my closed-backed Sony MDR7509 headphones, which have an impedance of 32Ω, and I could easily drive those to painfully loud levels. The same applied to Sennheiser HD25‑1 IIs, which are 70Ω, Beyer HD770 Pros at 80Ω, and AKG K271s at 55Ω, which is close to the optimum impedance for the Octo's maximum output power.

Setting mix balances is trivially simple, as is linking odd-even channels for stereo sources, and I liked the simplicity of plugging in my phone to access commercial tracks for practicing — although there are many other ways this external input feature can be useful.

Although the mixer panels have a 'wipe clean' plastic surface, care is required in choosing a writing implement, and I found an old-school chinagraph pencil was okay, although cleaning was a bit tedious. The Four Pack kit is supplied with a stack of five overlay cards for the mixer panels, which are great, but replacements would be an ongoing expense, and actually 10mm low-tack artists' tape is just as effective and a lot cheaper!

From both the engineers' and users' points of view, the Octo system is quite excellent. It's simple but well specified, very well built, extremely easy to install, it sounds great and has an extraordinary amount of volume. It's also expandable and incredibly easy to use. The only downside is the expense, which is quite high even for a four-panel system like the review set, and only a very well-heeled amateur or a professional working studio could realistically justify a full eight-panel set. That said, this is the kind of product that would have a very long working life and which makes every day in the studio (or on stage) considerably easier than it might otherwise be — and that could well be enough to sway many to hand over their credit cards. I enjoyed using the system very much and if I was asked to specify an artist's foldback system, the Octo would certainly feature highly on my shortlist.