Photo: Mark Ewing. This high-quality passive monitor controller can cater for five stereo input sources and three pairs of speakers, with built-in cue monitoring and talkback functions.
Presonus Central Station Plus Unboxing & First Impressions
With the continuing rise to domination of the computer workstation, and the corresponding demise of the hardware mixer, one of the major practical hurdles to overcome is that of monitoring — source selection, speaker control, talkback, cue feeds and so forth. A lot of people solve the problem by using a compact budget mixer, but these rarely incorporate all the facilities that are really needed and usually end up being an ergonomic nightmare.
When I had to address this problem several years ago I was able to persuade a broadcast mixer company, Audix Broadcast, to cobble a bespoke unit together for me based on long-established BBC monitoring functionality.
This unique unit has worked flawlessly for me ever since and I'd be completely lost without it, but clearly this particular solution is not an option open to most people.
A variety of connections for all of your sources and destinations.
However, several well-known manufacturers have realised the need in DAW-based studios for a versatile monitoring controller, and there are now several alternatives around across a wide price range. Some address the specialised needs of surround-sound monitoring environments Tascam DSM7. The Central Station has been designed as a very high-quality monitoring control unit, and is one of the most expensive in the short list of alternatives I gave above.
In general terms, it provides much the same range of facilities as the others: outputs to three sets of speakers with the usual dim and mono controls, five stereo inputs, metering, and separate cue outputs with talkback. However, this PreSonus offering is unusual in that the main signal path is completely balanced and entirely passive, and all the switching is performed with sealed relays 34 of them to be exact.
So the manufacturer's emphasis is firmly on the side of transparent sound quality with very little in the way to add noise, coloration, or distortion. They're talking my language! The unit is contained in a 1U rackmount box measuring 5.
Sadly, it employs an external 'line lump' PSU rather than having an internal mains power supply. Although I'm sure there are perfectly sensible technical arguments for taking the mains transformer out of the box in this way, I would still prefer an integral supply from the point of view of neatness and convenience. The front panel is brushed aluminium, while the rest of the case is painted black.
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The majority of the connections are on the rear panel, but there are two headphone sockets on the front. All the switches are illuminated with blue LEDs, and the control knobs are a nice knurled metal design, again painted blue. The panel markings are very clear and easily readable, even in dim lighting situations.
The rear panel is pretty crowded, but is clearly subdivided into the various sections. Next are six TRS quarter-inch sockets which provide balanced line-level outputs to feed three stereo pairs of active speakers or speaker amplifiers. The next section boasts another four TRS sockets which provide the Main and Cue monitor outputs, again stereo and balanced.
Analogue inputs are catered for with another four TRS sockets for two stereo balanced inputs, plus a pair of phono sockets for an unbalanced stereo input. A pin D-Sub socket allows a remote control unit to be connected see the box for more details , and the final section contains a three-pin female XLR for an external dynamic talkback mic, with a TS socket for a footswitch to activate talkback remotely.
There simply isn't space on a unit this slim to house XLR connectors for everything, so the TRS sockets are a good compromise and a lot more convenient than a row of D-Sub connectors. This is a really neat little controller, intended to sit on a desktop beside your DAW keyboard and mouse.
It measures 50 x x mm hwd, sloping down slightly at the front, and connects with the Central Station via a single pin D-Sub socket. The unit is powered entirely from the Central Station and no other connections are required. The remote is styled in the same way as the main unit, and shares the same illuminated buttons and knobs.
To control the Central Station, the remote must be activated by pressing a small button on the rear of the main unit. When this is done, a blue LED illuminates adjacent to the main volume control on the Central Station to indicate that the remote control is active, and a similar LED on the remote illuminates to confirm that it is now in control.
At the same time, the buttons illuminate to reflect the current source and output settings. These buttons all work in concert with those on the main unit, enabling source selections to be changed and monitoring parameters altered from either unit. However, the volume control can only be adjusted from the CSR1 when the remote is active — the control on the main unit is disabled and the balanced analogue signal is routed all the way out to the CSR1 and back!
Talkback is also built into the remote controller. As on the main unit, there is an internal electret microphone with its own volume control and a 'push to talk' button. This can be used instead of, as well as, and even at the same time as, the talkback on the main unit.
The front panel is very logically laid out and it's easy to see at a glance the status of everything. Like the rear panel, the various control sections are logically divided, starting on the left with the talkback functions, then the headphone outputs, the cue feed input selectors, the main input selectors, the bar-graph metering, the output selectors and controls, and the main volume knob. Although it might be an unusual approach, I'll describe the functionality of the Central Station by starting at the output end and working back towards the front.
PreSonus Central Station
Trust me, it should hopefully make more sense The unit can provide monitoring output signals for up to three stereo pairs of monitors labelled A, B, and C and illuminated buttons route the output to the required speakers, with an associated mechanical click from the box as the relays work.
Outputs A and B are exclusive — meaning you can only have one or the other, not both — and these would normally be used for the main monitors and the nearfields or nearfields and 'grot boxes' respectively.
The switching logic is quite sophisticated, ensuring that if you select output B when A is active, the latter mutes, and vice versa.
Pushing the button for the currently selected output again turns it off.
Any of the stereo pairs of speaker outputs can be trimmed by using a screwdriver to adjust the appropriate multi-turn pot on the front panel. It is intended for feeding an active subwoofer with built-in low-pass filtering , and allows the subwoofer to be switched in and out as required. It can also be used as a third monitor selector, of course, but there is no interlocking logic to kill the A and B feeds when C is selected. It would have been more flexible had there been an option switch somewhere enabling interlocking or independent selection for the C output, but it remains a useful facility nonetheless.
To the right of the speaker select buttons are six multi-turn trimmers which enable the outputs to be level balanced. The trimmers span a 90dB range.
The main monitoring volume control is at the extreme right-hand side of the unit, and is a high-quality multi-element potentiometer operating directly on the balanced monitoring signal. The panel markings around the knob show numerous subdivisions, but only the extremes are marked with level values 0dB and dB.
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Some users may find this frustrating, as it makes it slightly harder to reset the volume knob to a precise level setting. However, the clear white index mark on the knob itself helps to identify its rotational angle.
Below the three output selector buttons are three more illuminated buttons for output-signal conditioning. These provide Mute, Dim, and Mono functions, all provided through relays again. The first function seems rather superfluous to me, given the fact that the outputs can be muted simply by pressing the currently active output button anyway. The Dim button provides a 30dB attenuation and is activated automatically when talkback is used to prevent howlrounds.
The Mono button replaces the main stereo signal with derived mono created by a summing amplifier. This is obviously useful for checking mono compatibility and detecting any phase anomalies, as well as confirming the centre of the stereo image. However, a much better way to check mono compatibility is to listen to the derived mono on a single speaker, as mono on two speakers tends to give a misleading impression of the amount of bass.
However, the Central Station cannot accommodate this function. To be fair, very few monitoring controllers are this fastidious, although this is a great shame, as the difference in the mono monitoring techniques is not subtle! While I'm being picky, there is no phase-reverse facility here either — something which I find an essential monitoring tool. Since the Mute button is superfluous, maybe PreSonus would consider an updated version which replaced this with a phase-reverse facility — a relatively simple modification given the simplicity of the signal path.
Being able to invert the polarity of one channel of the monitoring is very useful. For example, sometimes being able to put the speakers deliberately out of phase is useful to identify the presence of a phase error elsewhere in the signal chain.
When trying to match the levels of two channels, such as when aligning a stereo pair, being able to invert one channel and then sum to mono to produce a cancellation null makes very fast and easy work of an otherwise fiddly process. Obviously, since the signal path is passive, the input impedance varies according to the setting of the various speaker output attenuators and the main volume control.
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The passive nature of the signal path also provides some unusual specifications, such as a signal-to-noise ratio of dB; a frequency response of DC to over 1MHz, and distortion of less than 0.
The input side of the Central Station is very simple and straightforward, with just four logic-interlocked illuminated buttons to select the required input source.
There are two balanced line-level stereo inputs which are routed straight through to the outputs via relays. The Aux input incorporates a buffer amplifier to provide a balanced line-level signal for the input selectors to work with.
The two digital inputs are very handy, and enables comparison of two separate sources through the same D-A converter — thereby providing a consistent reference sound quality. The output from the D-A is presented as a balanced signal to the input selection matrix to match the other sources.
There is no facility to match input signal levels at all other than at the Aux input , but I don't think that will present a problem to most users, and it's a small price to pay for the advantages of the straight-wire signal path.
The selected input source is not only routed to the appropriate speaker outputs, but also to a pair of TRS sockets on the rear panel as a balanced line-level recording feed.
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Clearly, the meter should not be considered an accurate alternative to a true digital meter, despite its markings, but it is useful to be able to view the programme levels, all the same. A second button associated with the meter is labelled Calibrate, and this caters for those who like to operate with some meter calibration other than the EBU recommendation.
The process is very simple: all you have to do is feed a constant tone into the Central Station at your nominal zero level, and then press and hold the Calibrate button for more than two seconds. The system then adjusts the internal calibration to accommodate the new level, showing this as 0dBu on the meter. The factory standard calibration can be recalled by simply turning off the Calibrate button, and the user calibration is remembered even after powering the unit off and on, until it is changed by holding the button down again for more than two seconds.
Pushing either of the headphone output knobs switches the monitoring source allocated to it between the cue and main mixes.
The Central Station provides more than just a monitoring controller; it also incorporates an independent cue monitoring system. The source selections are the same as those for the main input: TRS1, TRS2, Aux, and whichever digital input has already been selected.
There is also a main volume control and the selected signal is available on a pair of TRS sockets on the rear panel as a buffered impedance-balanced output. When talkback is activated the cue source signal is attenuated by 30dB so that the talkback can be heard clearly over it.
The current source cue or main mix is indicated by small blue LEDs beside each headphone volume control. This function is useful for control-room headphone monitoring, and extends the versatility of the Central Station significantly. Needless to say, the talkback signal is not present on the headphones if they are monitoring the main output.
The final control section is for the talkback facility. The unit incorporates a built-in electret microphone which is activated via a momentary non-latching square button. The talkback volume can be set with a front-panel gain control spanning a dB range.
The talkback can also be activated via a footswitch or any other closing contact switch connected to the rear-panel socket. An external microphone can be connected in place of the internal electret if required, but as there is no phantom power available a dynamic or self-powered mic is necessary. A rear-panel button disables the internal mic in favour of the external one. The BBC has a standardised and comprehensive approach to the requirements of loudspeaker monitoring controls, and it's informative to consider the arguments for its traditional way of working in the light of the new breed of budget controllers now becoming available.