TC Electronic D-two

Digital Delay

Published in SOS May 2000
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Reviews : Effects

A studio effects processor dedicated solely to providing digital delay is a rare thing in this age of all-singing, all-dancing multi-effects units. Paul White tries out TC Electronic's affordable D•Two.

Back in the early '80s, there were lots of dedicated delay/echo boxes to choose from, but most of these disappeared when programmable multi-effects units came onto the scene. Some musicians complained that they still needed a dedicated echo box with simple, quickly accessible controls — but as it was virtually as cheap to build a multi-effects box as a delay-only unit, these demands were largely ignored. There were exceptions, such as the high-end TC2290 (which is still in production today), but in the main, people learned to make do with what they were given.

Now, however, TC clearly think the time is right to build a dedicated delay unit more appropriate to the needs of today's marketplace without having to charge the premium price of their 2290, and what they have come up with is an interesting blend of established ideas and innovation.


The 1U-high D•Two is intended to be equally at home in live or recording applications, and follows a stereo-in, stereo-out format using balanced quarter-inch jacks and S/PDIF digital I/O on co-axial connectors.

TC D•TWO £459
Superb sound quality.
Unique rhythmic and partially reversed effects.
Well-thought-out operating system.
Flanger/Chorus is always post-delay.
TC have managed to produce an affordable and easy-to-operate echo/delay box that has true high-end audio performance as well as the capacity to produce a range of effects not offered by competing units.

Mains comes in via an IEC connector rather than the cost-effective but irritating mains adaptors used by some other manufacturers, and there's also a quarter-inch jack pedal input that can be used for tempo tapping, rhythm tapping or bypass.

There's a full set of MIDI In, Out and Thru connectors permitting patch loading and dumping, patch selection and real-time MIDI parameter control — all the unit's main parameters are pre-mapped to specific MIDI continuous controllers.

The front panel makes use of a large, three-colour illuminated display to aid programming and patch selection, while much of the control is done using the two large infinite rotary controller knobs. Traditional rotary controls are used to set the input level and effect/dry mix, while the remaining 16 buttons are arranged in logical groups to make operation more intuitive.

The sampling rate may be set to either 44.1kHz or 48kHz, while the use of 24-bit converters in the analogue stages provides a dynamic range of around 100dB. Where bit depths of less than 24 bits are required at the digital output, dither is implemented to maximise the dynamic range for 20, 16 and 8-bit output formats. There's no word clock facility, but that isn't surprising on a unit of this price. The setup pages allow the user to adjust both digital and analogue operating levels, select AES-EBU or S/PDIF data stream formats and to choose the sampling rate.

What Can It Do?

The market and musicians' needs have moved on since the early '80s, and it's no longer enough to offer an echo box that can only produce multitap delays with feedback. The TC D•Two can do all the basic stuff, and of course it's fully programmable, but its main claim to fame is its ability to create rhythmic delays. When set to rhythm mode, the user can tap in a rhythm of up to 10 beats (within the maximum delay time of 10 seconds), whereupon the D•Two will automatically create delay taps at these intervals to provide a rhythmic echo. The levels of these taps may be controlled in some interesting ways, which I'll get into later, and the speed of the whole rhythmic pattern can be scaled up or down without affecting the tap ratios. Furthermore, and this is something most of us will really appreciate, you can quantise the rhythmic tap positions to make the timing rock-solid. The rhythmic delay may be locked to incoming MIDI clock for arpeggiator-accurate timing.

In normal mode, more conventional equally spaced delays can be tapped in. Edit features have been incorporated to allow the delay time to be viewed or edited against tempo in bpm, rather than time, and the user can specify what subdivision of a bar the delays should run at. The D•Two is also adept at reverse delay treatments (see box).

Because of the extensive multitap facility, it's also possible to create echoes with a specific number of repeats rather than just allowing them to decay progressively, as is the case where a single repeat is used with feedback; a number of stereo enhancement treatments are also included. One of these enables the user to offset the timing of the two delay channels slightly to broaden the effect, while another allows one delay channel to be phase-reversed with respect to the other. Both these options can affect the mono-compatibility of the effects portion of the signal, so I'd advise anyone using them to check that their music still works OK in mono before mixing. More conventional ping-pong echo is also possible and the D•Two shares the 2290's dynamic delay feature, a ducking system that lowers the delay level when the input is loud and allows it to swell during pauses.

One requirement of a modern delay unit is that it should be able to sound like an old-fashioned tape delay, but ideally without the background noise or the sound of a rapidly ageing tape splice passing over the heads every few seconds. There are various degrees to which such emulations can be taken, but the main factors are the limited bandwidth of the recording section, distortion introduced by tape saturation, and tape-speed instability caused by worn parts. TC include variable filters (both high- and low-cut) in both the delay line and the feedback loop to simulate the way echoes thin out and become more indistinct as they are recirculated. The high- and low-cut filters are separately adjustable for the dry signal and the delayed signal, and if you're into emulating tape effects, it's interesting to note that the low cut is almost as important to the authenticity of the result as the high cut. The extensive multitap architecture means that just about any design of multi-head tape echo can be approximated.

The designers didn't feel the need to include a mechanism to add distortion to successive echoes, but they have put in a chorus/flanger section which may be used overtly as an effect, or more subtly to create the illusion of wow and flutter in the tape path. The chorus/flanger always comes after the delay section, though my preference would be to have it switchable pre/post as the two configurations can sound very different. For example, to emulate tape-echo wow and flutter, the pitch modulation should come at the input to the delay chain. On the bonus side, if you don't want to edit the chorus/flanger parameters too much, you can switch on the 'golden ratio' function, which means that as you adjust the mod rate, the depth automatically changes to a suitable value, and vice versa.

TC have included 50 factory patches to show off the various party tricks of which the D•Two is capable, as well as 100 user memories, but much of their effort has gone into making the control system as intuitive as possible. This extends to better-than-average metering, where in addition to showing accurate input levels for both channels (with overload warnings), there's also a gain-reduction meter to monitor the effect of the dynamic delay facility. As well as patch names, the display also shows delay time, feedback amount, filter status, ping-pong status and tap-time subdivision information. A couple of alternately flashing squares indicate the overall tempo against which your echoes are placed.

Specific Controls

The first rotary encoder is associated with two buttons labelled Delay/Tap and Feedback Rhythm. The first of these allows the delay time to be changed by the wheel or to be tapped in directly from the button. The second has three functions — when its LED is lit, the wheel changes the feedback level, but if the button is pressed and then held down, the wheel changes the number of repeats directly. Alternatively, tapping the button allows the creation of rhythmically spaced delay taps, as described earlier. This is by far the easiest method of setting up a delay time and pattern.

  Vehicle For Reversing  
  The D•Two's Reverse section hides a complete repertoire of unorthodox tricks to dazzle the unwary listener, and on guitar at least, most of these are far more musical and useful than you might at first expect. Obviously a reverse echo can't anticipate what you're going to play (though in my case it could probably make a fair guess!), then generate the echoes before you play the first note — instead, it plays back sections of material stored in the delay buffer in reverse order. But in true TC tradition, there is an impressive degree of flexibility. For example, you can opt just to have the first or second tap reversed while the rest carry on as normal, or you may want just the last tap reversed. Then again, how about just having the odd-numbered taps reversed, or just the evens for that matter? You can choose any of these options, or just have the whole lot come back reversed; either way, you can also set a level threshold below which your chosen reversal option takes place. How some of these variations will actually sound is less than obvious from just reading about them, so you need to play around a little, but I can guarantee that if you get hold of one of these boxes, playing around is something you'll be inspired to do a lot of.  

The Spatial button enables or disables the delay/phase-reverse stereo enhancement features; a really neat touch is that double-clicking this button takes you directly to the parameters relating to this function. This double-click shortcut system is used in various places throughout the interface and can save a lot of time and menu-cruising.

A dedicated Edit button gets you into what TC call the General Edit List, where the various process parameters can be located and edited sequentially. The Save and Recall buttons do much as you'd expect while Setup is used to sort out all those utilitarian things such as I/O formats, levels, MIDI status, sample rates and other global functions. Arrow keys are used to move the screen cursor, while the right-hand data-entry knob is used to modify selected parameter values. In all, navigation is pretty conventional and straightforward.

Bypass can be effected from either the front-panel button of the same name or from an optional footswitch, and may be set up so that the delay is either killed instantly or allowed to run its natural course.

Delay Feedback

I've already commented on the innovative rhythmic aspect of the delay taps and the very straightforward way in which these can be programmed by hitting the Rhythm button, but the feedback regime is also structured to allow the entire pattern to decay gracefully rather than disintegrating into a mess. Once entered, the tap spacing may be quantised against a user bar length (best tapped in directly) and a chosen number of divisions (for example, 16ths). The tap spacing may also be 'shuffled' to give the delay rhythm a degree of swing.

Yet another useful feature is that the decay characteristics can be selected as Normal, so that each successive repeat decreases in level, or as Step, where the whole rhythm pattern drops in level each time it goes around. Individual taps may be changed in level and the timing of each tap may be edited separately if necessary, but even this is very simple to achieve.

Ping-pong includes the ability to have delays coming from hard left and right or to pan during the course of one rhythmic cycle while dynamic delay is also quite adjustable with variable threshold, release and damping (ducking amount).

Playing Around

One of the first things I noticed about the D•Two is how clean and quiet it sounded, even with the flanger going full belt or with so much feedback that the delay pattern seems to recirculate forever. Using the filters thins out the echoes nicely for that distant, vintage sound, and there's no digital grunge or other nastiness to spoil the 'analogue' quality of the effect.

Tapping in new rhythms is simplicity itself, and if it doesn't work out quite as expected, you can either do the whole thing again or go into edit mode and vary the level and time for each tap independently. The current tap number is shown in the display, and the parameter dial may be used to step through each tap. Being able to quantise the delay rhythms and sync them to MIDI clock will obviously be particularly useful for anyone using a sequencer.

Dynamic delay works beautifully, and sounds quite smooth and natural so the delay can be made to swell up by just the right amount during pauses. However, it was the reverse treatments that really caught my interest. Used with guitar, they produce a complex, textural delay effect that can sound quite ethereal. With percussive sounds, the reverse effect is more obvious, as you might expect, and if reversing a tap makes the timing seem odd, you can always edit the tap timing until you get the feel exactly right.


In the D•Two, TC have produced a very attractive delay unit that sounds exemplary and offers some unique features as well as all of the expected ones. The rhythmic and reverse facilities are the most dramatic, but the friendly interface and variable filters make it easy to set up quite convincing tape-echo emulations as well as more routine delay treatments. I feel the modulation section should have been switchable pre-post delay, and a little tape-saturation emulation might have made the tape delay simulations even more convincing, but on the whole, the sound is faultless and the unit is lots of fun to use. If TC have any plans to update their commendably concise manual, might I suggest a page with the head spacing ratio details for all the popular tape-echo boxes? Whether you're into tight, rhythmic dance music or trance music, the D•Two is the echo box to go for. Nothing comes close at the price, and many of its features, such as the rhythmic and reverse treatments, are unavailable on any other unit, even the much more expensive TC 2290.

£459 including VAT.
TC Electronic
+44 (0)800 917 8926.
+44 (0)800 917 6510.
Click here to email

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