A professional surround monitoring controller for a variety of speaker configurations up to 7.1
Very few home studio desks, or even the smaller professional consoles, incorporate the necessary facilities for 5.1 surround monitoring so, for many, the ideal solution is a dedicated outboard monitoring controller which sits between the desk buss outputs and stem recorder, allowing either source to be monitored with all the necessary facilities. One of the latest such machines is the Tascam DSM7.1, a rather substantial 3U rackmount box which can handle 7.1, 6.1, 5.1 and LCRS formats, and incorporates facilities for inserting professional encode/decode systems (such as a Dolby Digital) as well. The unit boasts a comprehensive range of facilities for down-mixing (to LCRS, stereo and mono), has various bass management strategies, and the control surface can be detached from the main processor to use as a convenient remote controller.
The DSM7.1 is intended primarily for use with Tascam's DM24 digital mixing console and the company's various multi-channel digital recorders, although optional interface cards enable interconnection with equipment using other digital or analogue interface formats. The monitoring controller operates entirely in the digital domain, with 32-bit floating-point number crunching for all signal-routing and level-processing functions.
Eight buss outputs from your console are connected to the DSM7.1, either via the standard TDIF interface or through an alternative interface card installed in the first option slot, and are then routed internally to three destinations: a 'tracking recorder', a stem mastering recorder, and the monitoring system. The tracking recorder is not monitored, and this connection is provided to maintain the signal path to and from a multitrack machine when desk busses are used for both tracking and mixing. In the case of a 24-track system, for example, busses 9-17 and 18-24 can be connected directly to a 24-track recorder, but busses 1-8 need to go to the first eight tracks of the multitrack, as well as to the stem master recorder and the surround monitoring. The DSM7.1 takes such configurations in its stride, and so avoids any need to repatch cables. If the tracking recorder is not TDIF compatible, an alternative format can be adopted by installing a suitable card in the second option slot.
The returns from the tracking recorder are routed straight through the unit and back to the mixing console to enable monitoring, overdubbing and bouncing operations in the normal way. The stem master recorder interface is provided with TDIF, ADAT optical and AES-EBU interfaces, all outputs being driven simultaneously, but the appropriate return has to be selected as necessary (there is no analogue interface option here). The stem master returns are routed to the monitoring controller selector, so that either the console buss sends or the stem recorder outputs can be auditioned.
The third option slot is provided to allow an alternative interface card to be used to connect an external processor if the standard AES-EBU interface is unsuitable -- an analogue card is the most likely alternative, but only one analogue card can be installed in the DSM7.1 at a time. The TDIF and ADAT interfaces can only support sample rates at 44.1kHz and 48kHz of course, but if AES-EBU and analogue interface cards are installed, the system can operate at 88.1kHz or 96kHz as well. The system supports 24-bit resolution where appropriate and, as far as the recorders are concerned, what comes in is what goes out, so the interface is completely transparent. Clocking requires a little thought, as the DSM7.1 has no clock facility of its own so must be synchronised to either the console inputs, the stem master recorder, or an external word clock.
The monitoring outputs are provided on AES-EBU digital and analogue interfaces, with provision for eight separate feeds to accommodate formats up to 7.1. When configured for 5.1 or LCRS formats the last two outputs can be reassigned to drive an alternative stereo monitoring system. There is also a stereo analogue input to the monitoring matrix to enable integration with a desk's stereo monitoring selection. The final interface on the rear panel is a 3.5mm socket which provides remote dim and mute functions. A momentary closing contact between tip and sleeve mutes or unmutes all outputs, while a momentary closing contact between ring and sleeve dims or undims all outputs.
The detachable control panel is divided into three main parts. The Setup section to the left contains a large LCD panel with five dual-function system configuration buttons immediately below. A rotary encoder to the right adjusts selected parameter values and a pair of cursor buttons are provided for menu navigation. These normally offer left/right scrolling. A Shift key is provided to access the secondary configuration button functions, and also to switch the cursor buttons to scroll vertically instead of horizontally, although this last function is not marked on the panel or mentioned in the handbook.
The centre section of the panel is concerned with muting the individual speaker channels, and nine of the twelve buttons are laid out to represent the corresponding speaker positions. The middle of the three other buttons determines whether the speaker buttons mute or solo their respective outputs, and a menu option allows the solo function to be exclusive (ie. one channel at a time) or additive. If speaker outputs seven and eight have been reassigned to drive an alternative stereo monitoring system, then the top button activates this feed and mutes the surround outputs. The stereo signal is derived from the programmed downmix of the surround inputs. The final button routes the external stereo monitoring input to the main left and right speakers, enabling the desk monitor section to be auditioned, for example.
The third control section deals with the monitoring levels. The overall volume is controlled by a rotary encoder, and a two-digit display indicates the calibrated volume level. This is helpful in ensuring mixing is performed at a reference level. Two buttons here mute or dim the outputs, and a buss/return button auditions the desk buss outputs or the returns from the stem master recorder. The Downmix button can be programmed to combine channels into any desired alternative format, principally to check compatibility. By default, this function selects a stereo downmix, but could also be configured for an LCRS mix, if required. The relative levels of channels contributing to the stereo combination can all be adjusted. By pressing the Shift button first, the downmix function derives a mono mix instead, but this always seems to output a phantom centre across left and right, and there is sadly no option to route the mono mix to the centre speaker.
The last two buttons in this section activate the bass management function and switch on a calibration noise signal. The latter can be disabled to avoid accidental deafness and the former can be programmed to do one of two things. The first option is to remove the deep bass from the five main channels and route it all (in addition to the LFE signal) to a subwoofer output -- this enables small satellite speakers to be used or imitated. The second option is to route the deep bass from the LFE, centre and surround channels to the left and right channels to enable large left and right main speakers to be used with small satellites for centre and surround duties. Signal levels and crossover frequencies can be set as required in both cases.
Configuring the DSM7.1 requires a little planning, as the unit is extremely flexible, and therefore complex. For example, various technical parameters can be specified, such as the amount of attenuation applied when the dim function is activated, the reference monitoring SPL, the LFE and surround gain relative to the front speaker levels, and channel delays to compensate for the relative distances of loudspeakers.
The hardest aspect to grasp is that of setting calibrated reference levels (nominally 85dBC for film dubbing theatres and 82dBC for television dubbing theatres, but any appropriate value can be dialled in) and thereafter how to use the monitoring level control. However, the handbook is helpful in this regard, and the key point is that the volume control operates on the digital signal, so the amount of headroom is defined when calibrating the system level. Thus if the monitor system is aligned with the recommended -20dBFS reference noise signal to produce 85dBC, a peak 0dBFS signal will produce a sound pressure level of 105dBC. Turning the volume control down simply reduces the listening level, but turning it up will reduce the headroom within the controller, and 0dBFS signals will overload the output stages. It takes time to get your head around, but isn't a problem in practice.
I was able to integrate the Tascam DSM7.1 with a DM24 console, DA88 stem recorder, and monitoring system quickly and easily, and once I became familiar with it the Tascam DSM7.1 was a joy to use. The half share of cursor buttons was a frustration while configuring the unit, and I would have preferred an option to route a mono downmix to a centre speaker, rather than hearing it as a phantom image. Other than that, though, I had no complaints at all -- the machine did exactly what it was asked to do very well and the quality of the analogue monitoring outputs seemed marginally better than the analogue outputs of the console itself when the DSM7.1 was clocked directly from the studio master clock.