Newsgroups: rec.music.makers.synth
From: cassiel@cassiel.demon.co.uk (Nick Rothwell)
Subject: Fostex DCM100/MixTab MIDI mixing system
Date: Fri, 18 Dec 1992 18:52:59 +0000

Forwarded from SYNTH-L mailing list.
---
I presume this is the right mailing list for this kind of thing. Just a
quickie "first impressions" review since I've had these things wired up for
a few hours.

DCM100: 1U rackmount MIDI-controlled mixer, 8 stereo inputs (each of which
can be used as a mono input, but one stereo input is *not* two mono
inputs); in fact the entire mixer architecture is geared to stereo, with
stereo FX sends and returns (if your outboard FX box has only mono in,
you're a bit screwed since it'll only effect one side of the send). Pan is
just L/R attenuation. Each channel has low and high EQ (100Hz, 10kHz),
-15/+15dB. The EQ is actually quite nice for what it does, but it is
basically just bass and treble. What else: two effects buses (postfade),
BUT each channel can only send to one or the other, not both. I've
circumvented this by bringing some FX returns through other channels (of
which I now have plenty to spare). Otherwise, the aux bus architecture is
as you'd expect: level per channel, master send levels, return EQ (as for
the channels) and levels. Physically: quite a deep 1U rack (14" or so),
everything done via mono jacks so things are quite cramped on the back. The
only controls are trim pots on the front (which are actually quite hot:
line level inputs are generally well normalised at the lowest setting) and
power switch. There's a twin multi-segment LED for level (-10dB..+6). This
is output bus level; there's no input monitoring or clip LED's, which is a
shame. The front of the unit is a plastic shell, rather flimsy
looking/feeling.

MixTab: A fader box, basically. Eight channels (stereo ones), plus FX
send/return controls, master volume. There are pushbuttons for aux select
per channel (aux 1/2) and for channel mute. The faders have about a 2"
throw, maybe a little more; everything else is buttons + knobs. Oh: the
MixTab also allows scene recall and selection. The scenes (100 of them) are
stored in the DCM, *not* the MixTab. The DCM's take patch changes (audio
changes are then immediate, not faded), and the MixTab knows how to request
and store current setups. The MixTab is purely a MIDI controller, but with
some interesting wrinkles. Every control carries a two-colour LED (VRL:
Value Recognition LED, sic.). The LED flashes red if the MixTab control is
over the DCM setting, green if below, with blink rate indicating degree of
disagreement. The MixTab has a choice of pickup modes for matching and then
changing settings. The scheme isn't too bad to use. I'd say it'd be fine
for one DCM, but it's perhaps a little difficult to get used to when
driving two. (So, if that's a hassle, buy two MixTabs.) I intend to run a
MAX program between the MixTab and DCM's to give me clearer readouts, and
provide sub-scenes, algorithmic mixing and stuff. (For that matter, a
MixTab would make a decent generic MIDI controller source under MAX. Hmm.
Maybe an analogue sequencer panel?) A MixTab can drive three DCM's (on
consecutive MIDI channels). When selecting a different DCM, the MixTab
requests the (new) DCM's state and indicates discrepancies on its LED's.
You get used to the flashing lights (assuming your brain hasn't be totally
blown by the MixTab's psychadelic power-up sequence). There's some
zippering when changing volume levels and clicks when muting non-zero
volumes, so you have to keep volume fades slowish. The DCM's carry a
programmable smoothing function for this, but I didn't notice it doing
much. Physically the MixTab controls are good, with pretty decent faders.
The pushbuttons are the only naff part: shallow travel and flimsy feel,
like patch buttons on cheap synths.

Neither the MixTab nor the DCM100 has any kind of SysEx implementation.
EVERYTHING is controllers, including store and recall request. A bulk dump
is a screed of controller messages. Oh, the DCM's also take patch changes -
that's it. Great for MAX hackers like me, a blow for generic librarians.
Oh, if you're running two DCM's you'll need a MIDI merger: each DCM needs
to be able to transmit status back into the MixTab.

Onto the audio stuff. Line inputs only. As I said, inputs seem a little
high; not enough attenuation for some sources, perhaps. You'll want to ride
the levels high anyway (+3/+6dB) to keep the S/N high. The DCM's seem to
have very low distortion and take high levels fairly well. Aux send levels
are perhaps a little low at top wack, which is a shame if you're trying to
FX a low signal and keep S/N good on the aux loop.

Two (or more) DCM's are ganged together by using main and aux bus ins and
outs: three stereo signals. I'm actually ganging aux1 (MIDIverb II) across
both mixers, with aux2 local to each (QuadraVerb on one, LXP-5 on other).
One annoying thing is that the stereo bus levels aren't matched: mixer 1
appears about 6dB hot when it arrives on the bus to mixer 2 (which means
it's 6dB noisier of course), and the bus input can't be attenuated. I don't
know if the aux bus ganging has the same problem. I might have to bring
mixer 1 down a channel or aux return to mixer 2 to get round this.

Sound quality: no real complaints. Were I a real Hi-Fi propellor-head I
might comment about a very slight loss in the upper-midrange, or a tiny
muddying of the bouquet of the frequency response near the top, but these
seem pretty mild for a mixer of this class. I've been playing CD's through
it without noticing any loss of quality. OK then: hands up those who were
worried about the 78dB S/N ratio? Go to the top of the class. Actually, the
jury is still out here; I've only had the units wired up for a few hours,
and the entire studio is currently in piles on the floor pending arrival of
a couple of SKB racks, so I'm currently chasing down hum and noise problems
just like we seem to do in all the Team Metlay sessions. ("OK Nick, stop
that a second! Now do it again. Stop it again... Hey guys, I've found the
source of that hum, it's Nick's bagel.") All my rack units are just stacked
up, so they're earthing against each other via the case screws, and the two
rack-mounted Quantum disks for the sampler make a quite exquisite variety
of line noise when powered up unless the Peavey and MicroWave are set to
the same volume (gnnnnn). Perhaps it's an obvious observation, but I guess
a problem with rackmount mixers (MIDI'ed or otherwise) is their proximity
to other audio gear and noise sources. I'd be REALLY interested to hear if
this is a common problem with (say) Ranes and suchlike, or whether the
DCM's are susceptible to this, which would be a drawback with them. I won't
know until things are properly racked and I've spent some time balancing
levels and investigating properly. My general feeling though is that the
DCM's are a touch hissy. I don't think I'd want to mix and master a
commercial album through them, and I'd be wary of running them in complex
submix arrangements, but for the applications I have in mind (live
performance and some recording) the noise floor is fine... but only if I
can keep the noise floor down and eliminate the problems I've got at
present. A lot of it comes down to maximising send levels and minimising
return levels, and obvious woogy-woogy like that (I say "obvious", but the
fact that all sends are postfade makes such things nontrivial sometimes),
but apart from that I won't know how good the final S/N is until things are
racked and balanced properly. If anyone's interested I'll report back when
it's done.

I can't really draw conclusions until I've got everything balanced and know
the effective S/N. The main drawbacks (as far as I can see) are the lack of
unity between ganged mixers, and problems getting hot aux signals to
outboard FX on attenuated channels. The compromises in the architecture are
minor. The benefits are major: 8 stereo channels in a 1U space, and total
recall and automation via a quite respectable control module, plus loads of
performance and control possibilities using something like MAX. With the
arrival of an MTP-II tomorrow, I'm close to realising the CASSIEL Live Rig
'93: two SKB racks, each carrying a DCM and a MIDI Time Piece. Each rack
has a PowerBook, one running MAX, one running Performer, so that each can
see the entire rig and the other PowerBook. Each rack takes a MIDI control
cable (RS424) and mains input and delivers stereo output. Add a seven-cable
snake between the racks (mixer gang, plus MKS-70 feed to both mixers, plus
RS424) and that's it for external cabling.

Clever, huh?

                      Nick Rothwell  |  "Say, how many contemporary dancers
   CASSIEL Contemporary Music/Dance  |     are there in this bar?"
        cassiel@cassiel.demon.co.uk  |  "Dunno; count the Dr. Martens
        cassiel@cix.compulink.co.uk  |     and divide by two..."

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