PreSonus' eight-channel Firewire interface is the first to use Yamaha's much-touted mLAN protocol. How does it compare to the proprietary driver systems developed by the likes of MOTU and Metric Halo?
For a long while now, MOTU have had the Firewire audio interface market to themselves (and still do where OS X is concerned). Recently this situation has begun to change with the full commercial release of Metric Halo's 2882 Mobile I/O, and now the PreSonus Firestation. The Mobile I/O, as reviewed in SOS November 2002, offers class-leading audio quality and several notable features not found on the MOTU devices. The Firestation, too, has been designed with the need to find a market niche in mind.
The main difference between the Firestation and its rivals is its use of the mLAN protocol to handle audio, MIDI and clock synchronisation across the Firewire buss. mLAN has been much touted (see Paul Wiffen's articles in SOS August, September and October 2000) as the protocol which unites previous protocols in the same cable, making for simple yet highly adaptive and powerful studio cabling. Imagine connecting your laptop to an audio interface, a keyboard and a mixing desk, with full communication between all devices on the network, yet only one cable between each. The only protocol to offer this solution thus far is mLAN, and the Firestation is supported under Mac OS 9.x and Windows XP, with OS X support promised for the future.
The second main feature difference between the Firestation and its rivals is the presence and function of physical controls on the unit itself. MOTU's 828 does carry controls but can't be used as a stand-alone mixer. The Metric Halo unit offers a very flexible and sophisticated internal mixer, but requires the connection of a computer in order to control it. The Firestation, on the other hand, has been designed so that it can be used as a multi-channel line mixer without the need for an attached computer; this facility also adds real zero-latency monitoring when recording with an ASIO host such as Logic or Digital Performer.
The Firestation includes two preamps which are switchable between solid-state and tube driven. That's right: inside the hi-tech outer skin of this beast lurks a real 12AX7 vacuum tube, for adding "greater warmth and a richer sound or desirable distortion in extreme cases"! Next to the Neutrik combo input sockets are the dual-concentric controls for each preamp, the outer control being for 'solid-state' gain, the inner one for controlling the amount of signal routed through the tube. The inner control clicks when turned fully anti-clockwise to indicate the deactivation of the tube circuit.
Each control is accompanied by two switches, one for 48V phantom power, the other providing a -20 dB pad. Above each control is a three-LED meter, useful for indicating the presence of a signal of appropriate level and/or clipping.
All the controls on the front of the Firestation are dual-concentric, and as such protrude quite a long way from the front panel. In a live or mobile situation care would have to be taken not to damage the PCB of the device — to which the pots are directly connected — by accidentally knocking these controls. Indeed, the first review sample I received had taken a nasty knock in transit which had damaged the first preamp, and affected the operation of the entire unit.
To the right of the preamp controls is the Direct Patch Line Mixer, which consists of five dual-concentric controls. The first two pairs control the volume of the first four channels. The third and fourth pair control channels five to eight but in stereo pairs — that is, the inner control of each sets the volume for each stereo pair (5+6, 7+8) and the outer control determines the pan position. When the Firestation's S/PDIF input is selected it is routed through channels 7+8 at the expense of analogue channels 7+8. Similarly, when the ADAT input is selected it is routed through mixer channels 1-8 at the expense of analogue input channels 1-8 (and the S/PDIF inputs, which would otherwise use 7 and 8). This is because the Firestation uses only one of Yamaha's first-generation mLAN chips, which are capable only of eight-channel operation. However, PreSonus say that multiple Firestations can be daisy-chained in a Mac OS system, each adding eight channels per unit to the network up to a maximum of 32 (four Firestations). I only had one Firestation available for review, so I was not able to test this. Multiple Firestations are not currently supported under Windows XP.
The fifth control on the line mixer determines the volume of mLAN return channels 1-4, one stereo pair to each 'half' of the pot (panning is controlled in the host software's mixer). This is so that the ASIO host's playback can be monitored alongside the input signal(s). All 12 channels of the line mixer are routed directly to the main outputs and headphone socket for monitoring.
No mixer should be without input level trim controls to ensure that the correct level enters each channel, and that the ASIO host software's recording level meters correspond as faithfully as possible to the level in the channel. Eight Analog to Digital Line Level pots are accessible through the top panel of the Firestation via a row of small holes. Adjustment with a small Phillips screwdriver allows a 0dB reference to be matched to any external device within a range of 14dB.
The Master Control section of the front panel sports one dual-concentric control, for independent control of headphone and main output level control. This is accompanied by five illuminating buttons. Mixer engages the line mixer — if this is not depressed, only mLAN channels 1+2 will be present in the main out mix and the mixer functions are disabled, all levels being set by the host software. S/PDIF assigns the S/PDIF inputs to channels 7+8 of the line mixer. The ADAT button has a similar function, assigning ADAT input channels 1-8 to mixer channels 1-8, and also to TRS outputs 1-8, defeating TRS and S/PDIF inputs. ADAT to mLAN routes the ADAT input to the mLAN output going to the host software, while S/PDIF to mLAN has a similar function, routing the S/PDIF input to channels 7+8 of the mLAN output to the computer.
The final section of the front panel allows the setting of the clock source and relevant sample rate. Set to EXT, the Firestation will sync to an external source. This can be BNC or ADAT input, or mLAN clock source from a connected computer. It should be noted at this point that Yamaha's first-generation mLAN chips only support 44.1 and 48 kHz sample rates, which are chosen in the mLAN control panel on the computer. When set to INT, the Firestation will provide word clock sync for other devices at 32, 44.1 or 48 kHz.
The back panel of the Firestation, like the front, has a number of significant differences from other Firewire audio devices. Working from right to left, the first pair of sockets is the main outputs on quarter-inch TRS jack sockets. To their left is a pair of direct outputs from the preamps allowing external dynamics processors to be placed in the signal channel. The output of any such device would be connected back to the line inputs, of which there are eight on quarter-inch balanced TRS sockets, to the left of the preamp sends. Next come eight balanced TRS quarter-inch line output sockets, followed by a footswitch input. This operates on MIDI channel 16 with controller 23 set to value 127, and could therefore be used to switch any connected device which can be made to respond to this.
BNC word clock in and out connectors are next, followed by the ADAT optical in and out. Unusually, these do not double up as optical S/PDIF in and out. S/PDIF signals are sent and received via a breakout cable that connects to the nine-pin D-sub connector to the left of the ADAT terminals. The S/PDIF connectors are co-axial, requiring the use of a converter such as M Audio's CO3 to connect optical equipment. The breakout cable also carries standard five-pin DIN MIDI In and Out sockets.
Before the IEC power supply socket and the Power switch are two Firewire (IEEE 1394) sockets. Having a spare socket enables the connection of a hard drive or further mLAN device (such as another Firestation) in case the host computer only has a single socket.
Included in the package are MIDI and S/PDIF breakout cables, a mains lead, a small user's manual and an installation CD for both Mac OS 9.x and Windows XP. The drivers on the disc I received were the same version as those on PreSonus' web site.
The Mac installer created three extensions called mLAN Driver, mLAN Expert, and mLAN Family (the addition of these requires a restart following installation in order to gain their functionality), along with the mLAN control panel and, in the mLAN tools folder created during this process, an application called mLAN Patchbay. There is also an mLAN ASIO driver which should be manually copied from this location to the ASIO drivers folder of your host software. You should also install OMS (which is not supplied, but is available as a free download from www.opcode.com/downloads/) if you wish to use MIDI via the Firestation. The OMS mLAN driver is also found in the tools folder and should be copied to the OMS folder within the system folder.
Software installation must occur with the Firestation disconnected but it must be reconnected before boot-up if the Patchbay setup is to work, since each Firestation has its own unique identity. Patchbay is a Yamaha application (supplied as part of the mLAN software package) which allows the virtual connection of the eight channels of the mLAN driver with the eight input and output channels available in the mLAN protocol. Connection is achieved by dragging the 16 items in the To (input) column up so each MacDriver item is opposite the corresponding PreSonus channel item in the From (output) column and vice versa. The screen shots on the previous page show the mLAN Patchbay application 'before' and 'after' connection.
Similar actions are carried out in the MIDI and word clock panes of the Patchbay. To effect your changes you then hit Apply and finish by saving your setup on the desktop. This last is necessary because the recommended boot procedure is as follows: connect the Firestation, boot up computer, open your Patchbay setup and hit Apply.
The latest version of the drivers supports multiple Firestation connection (by daisy-chaining from the Firewire sockets), and each interface in the network would require a discrete Patchbay setup.
Most ASIO drivers I have seen allow the number of samples per buffer to be set within a given range that controls the input/output (or patch-through) latency of the system. The numbers are usually (but not always) powers of 2, reflecting the binary basis of their function. The lower the samples-per-buffer figure the lower the latency. At 44.1kHz sample rate, for example, a samples-per-buffer figure of 64 would give a latency of 64/44100, or 0.0015 seconds (1.5 milliseconds).
The mLAN software that comes with the PreSonus allows an altogether more complex level of control. On the mLAN control panel (see screen shot, above right) there are settings for Buffer Length (in milliseconds) and Numbers of Buffers for both Send and Receive mLAN activity. The ASIO mLAN control panel available from within the ASIO host (by clicking Control Panel in the ASIO section of Logic's Audio Hardware and Drivers dialogue box for example) allows the settings of Preferred Buffer Length in milliseconds.
Yamaha divide patch-through latency into two parts. The first, Transmission, is the total of the latency caused by the ASIO mLAN driver plus the latency caused by the mLAN driver, ie. the Preferred buffer size (ASIO) plus (Send Buffer Length x Number of Buffers). The second, Reception, is the latency caused by the ASIO mLAN driver, whose minimum length is defined by the Receive Buffer Length in the mLAN Control Panel. It should be noted that although this does allow for a wide range of buffer sizes and resultant latencies to be controlled, less technically minded musicians might find this array of settings bewildering, and you're unlikely to be able to achieve the sub-5ms latency values that some ASIO hardware is capable of.
To change settings in the mLAN control panel it is necessary to quit the ASIO host, make the setting then hit Apply on the Patchbay. You would then relaunch the sequencer, open the ASIO control panel and make the Preferred Buffer Size adjustment — which requires you to again quit the application and relaunch to effect the setting. Some default settings and a recommended process for setting up a system were forthcoming from Yamaha via PreSonus, but they are not as yet available on the web site or in the instruction manual.
Using the Firestation with my trusty iBook 600, 44.1kHz 16-bit mono 'continuous' files playing back in Logic from an external fast Firewire drive gave the track counts in Table 1, below. Recording eight tracks via the eight inputs of each device, at the same time as playing back the above tracks gave the results in Table 2.
Table 1: MOTU's 828 outperforms the Firestation in the number of tracks it can play back from a Firewire hard drive.
Table 2: Figures measured when recording eight tracks while playing back show a similar discrepancy.
Changing buffer settings on the ASIO and mLAN drivers had negligible effect on these results, and the obvious conclusion to draw is that mLAN as a protocol does not work as efficiently as native Firewire for transmitting audio data. It is difficult to tell whether it is the protocol itself or the relatively undeveloped software (version 1.0.4 for mLAN against version 2.8.5 for Mac OS Firewire extensions and version 2.11 for MOTU's Firewire drivers) which is responsible for this situation.
It is fair to point out that mLAN is designed to carry other streams of data (such as MIDI) but it was not my understanding that bandwidth was reserved in the protocol at the expense of the audio stream. According to Yamaha, the current mLAN data rate of 200Mbps supports a theoretical maximum of 100 audio channels, while the forthcoming second generation of mLAN chips will operate at 400Mbps.
The second unit I was sent for review displayed a few quirks when the mixer section was engaged: mLAN return channel one was doubled at analogue channel one of the mixer, and a small amount of crosstalk was noted on channel four, bleeding from mLAN return channel one. Neither of these faults occurred with any other mLAN return channel. It is assumed that this was an isolated problem that will be ironed out in general production models.
MIDI In and Out via the breakout cable worked with no problems once OMS had been set up to recognise mLAN as a MIDI device. I was keen to test this further using an mLAN-equipped keyboard such as the Yamaha Motif or Korg Triton, to experience an mLAN network in operation. I was, however, disappointed to learn from Yamaha that they do not currently sell any mLAN equipment in the UK, although they say that they expect this situation to change in 2003. I also contacted Korg, who told me that mLAN was currently very difficult to sell in the UK, an mLAN board adding some £700 to the cost of a Triton. For this reason they were unable to obtain stock for evaluation. However, the technical team at PreSonus have a test rig which includes a Yamaha Motif and have reported no problems.
My current favourite testing application, ChannlD's Mac The Scope, unfortunately fell foul of a conflict with the ASIO driver. Yamaha's decision to allow buffer settings in milliseconds was not appreciated by the Scope's requirement to see buffer settings in powers of two samples per buffer. To be fair, Mac The Scope has proved very picky about ASIO drivers, MOTU's 828 driver causing it to crash on launch! The only reading for the Firestation that I was able to record, after much fiddling trying to make buffer settings compatible, was for its noise floor which came out at a very respectable -124dB against digital full scale (using 1024-point FFT).
Plugging a mic into one of the two channels with preamp controls, I made a few test recordings to check out the effect of the Tube Drive circuit, which utilises one 12AX7 'bottle'. With appropriate gain settings, this added a smooth warmth and subtle compression to the sound, pushing to a slight 'edge' at the limit of its operation (although background noise did increase significantly at this point). To the author's ears, jaded by digital cleanliness, it was gratifying to be able to dial this in at source (and monitor at zero latency) without the necessity to use either a vocal channel or mixing desk. Nastier distortion settings are obviously not the province of this feature, as the unit makes no pretensions as a guitar preamp or effects box.
In use, the sound quality of the Firestation is not at the limit of what is achievable in comparable devices, but in terms of spatial clarity and depth is certainly on a par with MOTU's 828, with which it might be compared if highest supported sample rate were the only yardstick. The Firestation, however, is aimed more at a market who would not rate bleeding-edge sound quality and sample-rate support beyond the capability of the rest of their system above more practical considerations. With an onboard mixer, mic preamps and a valve, and the option to be used as a stand-alone mixer to ADAT, the Firestation is attempting to address some of the more practical requirements of the recording community. mLAN is the protocol that PreSonus have chosen to implement their design, and while it seems to have some drawbacks as far as raw performance is concerned, it does mean the Firestation could be part of a perfectly integrated studio network.
Yamaha's UK distributors were keen to point out that mLAN is at the centre of the future direction of their computer music strategy. They have a "significant" number of mLAN-based products in the pipeline that will be brought to market when they consider that the "whole network" is ready to go. In particular, it seems that they are expecting a new generation of mLAN chips which will support sample rates up to 192kHz and up to 32 I/O channels per chip. There is much conjecture over the development of these new chips and support in future versions of Mac OS, and we shouldn't have long to wait before hard information is available. The current lack of mLAN support in the UK is a serious issue for those considering this interface, but when Yamaha does move to market, the Firestation will make a lot of sense to those trying to rationalise the increasing number of protocols currently necessary to 'connect' a studio.