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TL Audio M4

Valve Mixer By Hugh Robjohns
Published December 2005

TL Audio M4Photo: Mark Ewing

This new mixer caters for those who found TL Audio's M3 too small, and the flagship VTC too big. But is the M4 just right?

TL Audio are well known for their various ranges of hybrid valve and solid-state audio processors. They are also one of a very small set of manufacturers still making valve-based mixers. Although TL Audio's consoles are not 'true' valve desks, they manage to achieve modern performance specifications with classic 'tube' sonics at pragmatic prices by using hybrid designs combining solid-state electronics with dual-triode valve stages. Purists might hanker for designs that only employ valves, but in reality achieving modern performance expectations with all-valve designs costs far more than even the most fanatical are now willing to pay.

The company's first offering in the valve console market was the impressive VTC desk (reviewed back in SOS February 2000), which has acquired a strong reputation. Its baby brother, the M3 8:2 tracking console has also become a popular addition to more affluent DAW-based home studios, maintaining much of the design ethos and sonic quality of the VTC, but in a smaller and more appropriate package. The new M4 is a larger and slightly more sophisticated version of the M3, on which it is closely based, neatly bridging the gap between the M3 and VTC.

Like the M3, the new M4 is essentially a tracking and stereo mixdown console. It is available in three frame sizes from 16 to 32 channels, and I reviewed the 24-channel version. The input channels are constructed in sub-frames of eight strips which bolt either side of a narrow master, control, and output section. An external (and quiet — hurrah!) 2U rackmounting power unit supplies 300W into the biggest 32 channel frame, and 200W into the smaller 16 channel console. A two-metre connecting cable is supplied as standard.

The console is raked at a comfortable angle that allows all the control settings to be seen easily, and the controls themselves are well spaced and easy to adjust. In fact, the whole style and ergonomics are reminiscent of a console from the '60s or early '70s, with lots of space between the nicely weighted knobs and the man-sized buttons. Everything feels solid and well built, right down to the oiled oak end cheeks and armrest. Everything, that is, apart from the faders, which feel strangely lightweight and insubstantial compared to the rest of the controls.

Connections & Digital Interfacing Options

On the rear panel, the mic inputs and main stereo outputs are on XLRs, but everything else is on balanced TRS jack sockets. Most inputs and all outputs are individually switchable for +4dBu or -10dBV operation, which allows easy connection with a range of pro and semi-pro gear. A nice touch is that each channel features an insert point with separate balanced send and return sockets.

Optional DO8 digital boards can be installed in each input module to provide ADAT lightpipe I/O for simple connection to a DAW or other recorder, and an optional DO2 card can be installed in the master section to provide an S/PDIF stereo output. The latter has a fixed 24-bit word length, but the sampling rate can be selected from 44.1, 48, 88.2, or 96kHz. Each DO8 and DO2 card is entirely autonomous, but external word-clock inputs are provided for synchronisation.

Rather unusually for a console of this size, the M4 has no groups and no buss-routing facilities, other than to the main stereo outputs. If you want groups and routing you'll need to move up to the VTC. Instead, every channel has a direct output that also feeds the optional DO8 card's A-D converter. This direct output can be switched before or after the EQ, and is independent of the channel fader and Mute button. A dedicated Track send-level control optimises the headroom of your recording device, providing ±15dB trim and a maximum output level of +22dBu — sufficient to fully drive any professional A-D converter.

While this direct output arrangement is great for tracking, allowing every channel to be recorded separately to 'tape' with or without EQ, it does complicate things slightly when it comes to overdubbing at a later date, or when building up a mix by recording each track in isolation. You either have to re-connect the mic to the appropriate channel to access a specific track on the recorder, or you have to re-allocate inputs on your DAW. Neither is ideal for anyone accustomed to the flexibility of buss- or track-routing switches.

Channel Facilities

Each input channel has separate mic and line inputs (the DO8 card returns being normalled to the line inputs) selected with a front-panel switch, so that a multitrack recording can be remixed through the console simply by flipping all the input source switches. The mic input section affords a gain range of 44dB from +16dB to +60dB, and includes a switchable 30dB pad — it sounds a lot, but with a minimum gain setting of +16dB, a hot kick-drum mic could exercise the full 30dB of attenuation on offer.

TL Audio M4Photo: Mark EwingEvery channel has individual phantom-power switching, but the button is tucked away on the rear panel next to the input XLR, and with no indication on the channel strip to confirm whether phantom is switched on or not. A polarity reversal switch and 90Hz high-pass filter (12dB/octave) apply to both mic and line inputs. The line input features a gain swing of ±20dB, with a maximum input level of 26dBu — more than enough to cope with the hottest of D-A converter outputs.

The rest of the channel facilities are very similar to those of the M3, except that where the smaller console had two aux busses the M4 boasts four, the first two independently switchable pre/post-fader and the last two permanently post-fader. The EQ section is identical, with fixed-frequency high (12kHz) and low (80Hz) shelf equalisation and a pair of swept mid-bands (50Hz-2kHz and 500Hz-18kHz). The whole EQ section can be bypassed, and the ±15dB gain controls are all centre-detented. The two shelf equalisers have unusually steep slopes at 12dB/octave, although they work very well in practice, and the mid-band sections have a bandwidth of 1.5 octaves (corresponding to a Q value of 0.7), which is narrow enough to allow precise tonal correction without sounding too peaky. The insert point is normally pre-EQ, but can be switched post-EQ from the front panel, and the return can also be switched out of circuit if required.

Channel Mute and PFL buttons (with LEDs) are mounted on the fader panel above each 100mm fader, along with yellow Drive and red Peak LEDs. The Drive light gives some idea of how hard the valve in the input stage is being driven, glowing progressively brighter with signal levels between +6dBu and +16dBu. The harder the input stage is driven, the greater the characteristic harmonic distortion the valve provides. The red Peak LED illuminates at +21dBu, 5dB below the actual clip point, and indicates the peak-level signal monitored at the input amp and post-fader buffer of each channel. The desk has an impressive internal headroom, but I found that when it did finally clip it did so in a way typical of solid-state op amps, rather than giving the benign crunch of an all-valve design.

Output Section

The reasonably well-equipped input channels are, to my mind at least, let down slightly by the rather limited facilities of the narrow output section. Starting at the top, a pair of retro-styled round VU meters (with individual calibration trimmers recessed behind the front panel) are assisted by separate Peak LEDs. These meters follow the monitored signal, so indicate the two-track return or PFL channel levels instead of the mains stereo mix when appropriate. The main stereo mix output level is controlled with a pair of 100mm faders, spaced in the same way as the channel faders, and with the same 10dB of gain in hand. The main outputs are equipped with an insert point to allow the easy patching of a buss compressor, for example.

The four Aux Master output-level controls each have associated PFL buttons and LEDs, and there are two stereo effect returns with level and balance controls and PFL buttons. If a signal is patched only to a left effect-return socket it is automatically normalled to the right as well, providing a centred mono return which can then be panned as required.

The main monitoring level control has a delightfully large knob which is associated with a Mute button and a two-track return switch. There is a separate volume control for the headphone output (located on the fader panel next to the main faders), and the headphone output signal is always the same as that driving the main monitors. A PFL level-trim knob is provided to allow the monitoring level to be matched between the full mix and a soloed channel (over a ±20dB range). The only other facility on the control section is talkback, with an unpowered XLR socket, a volume control, and a pair of routing buttons. These allocate the talkback signal to either or both of the first two auxes.

TL Audio M4Photo: Mark Ewing

These master-section facilities are the minimum that would be required, and I would expect many potential customers to find them frustratingly basic — even the cheapest stand-alone monitor controller offers a more complete palette. For example, why is there no power to the talkback mic socket, when phantom is provided throughout the desk anyway? Although suitable dynamic mics are available, there are also a lot of electret gooseneck designs that require power. Why no facility to slate talkback to the main outputs? Why no facility to route the main stereo mix, two-track return, or effect returns to the aux outputs? Why no Dim control on the monitoring? Why no mono-check facility? Why only a single two-track return and no secondary monitor output? It's all a bit underwhelming and inflexible for a console in this UK price bracket.

Another concern I have is to do with the output faders. In the first instance, their wide spacing makes it extremely difficult to keep the stereo image stable when fading up and down — even if you use a plastic fader clip or the infamous 'pencil and sticky tape' alternative! It is also most unusual to have 10dB of gain available above unity in a master fader, and this makes fading up less straightforward than it would normally be, as well as allowing one fader to be knocked relative to the other more easily, resulting in off-centre images on the main output too. There's nothing as reassuring (and easy to check) as having the main output faders pushed up hard against their end stops. Overall, a single ganged stereo master fader, with unity gain at the top, would have been far more practical.

In The Studio With The M4

The M4 has many appealing features, and the control-surface ergonomics are excellent. In particular, having plenty of space around the controls means you can adjust things without having to use a pencil sharpener on your fingers first! All the controls feel like high-quality units, and there is only the faintest of clicks when switching the inserts and EQs in and out of circuit. Although, as I mentioned earlier, the faders feel light and flimsy in comparison to the rotary controls, they are silent in operation and deliver the goods well enough.

The overall sound quality is typical TL Audio, nicely warmed by the high-anode-voltage valve circuitry, but not overblown at all. Of course, cranking up the input levels drives the input-stage valve harder to deliver a much richer, more obviously 'valve enhanced' sound. However, while this can be useful for the odd effect, the real strength of the console is in the very subtle addition that the valves make when operating at more conventional levels.

The input section struggles a little to provide enough gain (or a low enough noise floor) to cope with low-output ribbon mics, but with typical condenser and dynamic mics coupled with normal close-miking techniques the 60dB on offer is perfectly sufficient. The mic input EIN specification figure of -127dBu is not the best around, but is quite respectable for a console stuffed full of valves, and more than adequate for the applications this desk is likely to find itself employed in.

While I'm reciting specifications, the overall distortion from line input to main output is quoted as 0.4 percent. This is a pretty high figure compared to most modern solid-state equipment, but it is entirely commensurate with the design intention of the console — it is a deliberately 'coloured' desk, and the distortion is mainly comprised of second harmonics generated by the valve stages. The output noise is quoted as a rather modest -72dBu, but if the output levels are being driven fairly hard (as they would have to be to fully modulate the input to a professional A-D converter) you could add easily another 15dB to that figure.

The EQ section is excellent, always sounding musical and complementary, but with sufficient bite and overlap in the swept mid-bands to really get to grips with any tonal source deficiencies when necessary. Switchable bandwidth on the mid-bands — as available on the VTC — would have been a nice additional feature, but that really would have been only the icing on an already very tasty cake. Its nice that the EQ bypass button was retained too , because so many desks leave this vital facility out, and the ability to bypass and reposition the insert point is also welcome. The separate balanced connections for the send and return also make life easy — so much better than having to use unbalanced 'Y' cables — and the ability to fine-tune the direct output levels from the console surface is a very worthwhile feature.

Four aux sends should be enough for most applications, especially given that a lot of people tend to use internal DAW plug-in effects rather than outboard processing and reverbs these days. Clearly, the desk is designed such that the first two auxes can be used for headphone cue mixes. However, this facility turns out to be frustratingly difficult to use in many situations. For example, there is no easy way of routing the main stereo mix or the two-track return to the appropriate aux outputs. Similarly, if you are using outboard reverbs, it would make sense to bring them back to the desk via the two effect returns, but there is no way you can then apply a little reverb to the headphone cue to help a vocalist.

A VTC For The Masses?

It seems a shame that a console with so many good points should have an impractical master-fader configuration and such a surprising lack of flexibility in the monitoring section. To me this is the ha'porth of tar that has spoiled this particular ship. The front end of the console is excellent for its intended task — the channel strips are well equipped and sound superb, and although the routing arrangements (or rather the lack of them) force a specific way of working, I don't see that as a significant practical problem at all. Essentially, the front end is a bigger and more flexible version of the M3, and an ideal large-scale tracking mixer for working with a DAW or hardware digital recorder.

However, whereas limited functionality might be acceptable in the monitoring section of the compact M3 — and a separate monitor controller is a reasonably practical and affordable solution — this cannot be true in a console as large and relatively expensive as the M4. Most of the facilities anyone would reasonably expect are all provided in the VTC: switching for alternative speakers, mono check, multiple external monitoring returns, the ability to slate talkback to the main output, source selection, and effects-return routing to cue-mix headphones — so it's not as if this is uncharted territory for TL Audio.

So overall, then, the M4 is a qualified success. Fabulous sound, solid construction, nice ergonomics, good input handling facilities, and excellent I/O flexibility. Balanced against that is a disappointing monitoring section and some frustrations in terms of the main outputs and headphone cue-mix provision. If the M3 doesn't offer you enough input channels and the VTC is too expensive, the M4 may be the ideal solution, and it is certainly the antidote for anyone who feels that digital recording still sounds too sterile and pristine. 


  • Characteristic TL Audio sound.
  • Excellent build quality.
  • Musical and controllable EQ.
  • Optional digital I/O cards.
  • Separate sockets for insert sends and returns.
  • Switchable I/O operating levels.
  • Nice, spacious control ergonomics.
  • Competitive UK pricing.


  • Poor monitoring facilities.
  • Split master output faders.
  • No groups or routing.
  • No slate talkback.


The M4 fills the gap between the M3 tracking console and the full VTC flagship, providing up to 32 channels with versatile and musical EQ, excellent I/O facilities, and old-world ergonomics. The output section is disappointingly limited, but for many the console's distinctive sound quality will outweigh its monitoring deficiencies.


16-channel model, £4694; 24-channel model (as reviewed), £5869; 32-channel model, £7044.

TL Audio +44 (0)1462 492090.

+44 (0)1462 492097.