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SPL Transient Designer

Dynamics Processor By Paul White
Published October 1998

SPL Transient Designer

SPL are renowned for producing highly specialised audio processing tools, and their latest product is no exception. Paul White attempts to unravel the mysteries of the Transient Designer dynamics processor.

SPL are best known for their slightly oddball Vitalizer product range, but even they are at a loss when it comes to describing the Transient Designer. It offers a new type of dynamic control, and though it is related to both the compressor and the expander, it could not fairly be described as either. Outwardly, the box is pretty conventional with balanced XLR audio inputs and outputs plus SPL's distinctive 'squirdly' blue front panel, but this simple exterior belies the complexity of what's taking place inside. The circuitry relies on VCA gain control technology, but there's a lot more to the process than compression — it can change the envelope of a sound, but it's not an envelope generator, and though you can use it to add punch to a mix, it's certainly not an enhancer. It's perhaps best to think of the Transient Designer as a 'results‑oriented' device insomuch as it's what it achieves that's important, not how it does it.

From the user's point of view, the Transient Designer is disarmingly simple to use — each channel has just an Attack control, a Sustain control and a Bypass button. Two further buttons are provided so that channels 1/2 and 3/4 can be linked as stereo pairs for processing stereo signals, and each channel has a Signal Present LED that comes on at input levels above ‑40dB. In fact, it's what you don't see that provides the clue as to how clever this box really is. There are no meters, no threshold controls, no ratio knobs and no make‑up gain controls. The process is independent of input level, and the two controls are so cleverly linked to the internal magic that setting up can be done entirely by ear.

So What Does It Do Exactly?

SPL Transient Designer

The rationale behind the box is to give the user direct control over the attack and sustain characteristics of natural sounds, and though this sounds less than revolutionary, you only have to play with the unit for a few minutes to realise that the Transient Designer is a very powerful creative tool. For example, you can take a gutless, flabby recording of an unremarkable drum kit and dial in some really hard‑hitting attack or, conversely, take a very percussive sound and soften the attack. You can also use the sustain control to work on the decay portion of sounds, and with drums you can tighten up the sound to give a fast, dry decay or you can make them ring as though you'd taken the dampers off the kit. It's just like having remote control over the amount of damping tape stuck to the drum heads — after the recording. What's more, because the process is independent of level, the effect is consistent regardless of whether the input signal is loud or soft, and off course you don't have to use it only on drums. How is it possible to achieve all this with just two controls?

The secret is something that SPL call Differential Envelope Technology (a registered trademark of course!), which works by using two envelope generators for the attack and two more for the release. On the attack side, one generator follows accurately the original signal amplitude while the second does the same thing but with a slower attack. Subtracting these envelopes produces a control signal that can be used either to increase or decrease the level of the audio depending on whether the Attack control is turned clockwise or anticlockwise from its centre position. A similar methodology is used to derive the release control envelope. The outcome is that any attack transients can be cut or boosted by up to 15dB and the sustain can be increased or decreased by up to 24dB.

The audio signal path is exceptionally clean with a THAT 2181 used as the gain control element. High‑quality input and output stages using laser‑trimmed resistors have been designed to produce minimal distortion plus an exceptionally high common mode rejection (CCMR). Relays bypass the channels completely when the power is off or when the channels are bypassed, and the dynamic attack/sustain time constants respond to the dynamics of the input signal to provide a musically natural result over a wide range of input material.

Designing Transients

So much for the science, but does it really leave your hair clean and shiny? To get the Transient Designer up and running, you need only patch it into an insert point and make sure you have enough input level to get the signal LED flashing. With both the Attack and Sustain pots set at their centre positions, there's no effect when switching the process in, but as you advance the Attack control, percussive sounds become more assertive with a snappier attack. Conversely, if you wind the Attack control back from centre, the attack of the original sound diminishes, but in a way that is still reasonably natural. The effect is definitely best appreciated with drums or percussion, but percussive bass lines also respond well to treatment.

The Release control has more range than the Attack control, and as you move the control anticlockwise, the sound dries up, tightens up and exhibits a faster release time. If you go too far, the sound takes on an 'expanded' characteristic, but used carefully, you can take the ring out of a badly set‑up drum kit and still leave it sounding natural. Take the control clockwise and the ring of the drums is enhanced. Some of you are probably thinking that you can create effects like these with any good compressor, but that's not entirely true. Certainly, if you're dealing with a single drum hit, you can use a compressor to modify the attack and release characteristics, but if the next hit that comes along is a radically different level, the effect of the processing changes. With the Transient Designer, every percussive sound gets the same treatment, regardless of level, and that's the secret of both its sound and its ease of use. Indeed there's so much range that you can take a kick drum sound and either sharpen it up to sound like a heavily processed drum machine kick, or you can pull back its attack, extend its release and make it sound like a 'bouncing basketball' electronic kick. Similarly, you can take an electronic kick and modify it so that it sounds almost like a real acoustic kick.

It's easy to use, it can seriously reshape percussive sounds and it's hard to make the Transient Designer sound anything other than musical, but are there any negative points? Well, you do have to be careful when recording to a digital destination, because as you add more attack to a sound, you increase its peak level. This is the opposite of a normal fast attack compressor that's set up to reduce the dynamic range of a sound. It's really not a problem, you just have to be aware of it, and in some cases, the subjective level of the treated sound will be lower than that of the untreated sound because of the extra headroom needed. On the other hand, you can take down the peak level of an over‑aggressive drum sound and increase your subjective level for a given headroom, so it all depends on how you use it. The really great thing is that you can check different settings instantly simply by moving two knobs — you're not constantly adjusting thresholds, selecting ratios or messing with attack and release times. What's more, because of the way the Attack and Release controls work, you effectively have the option to use different degrees of compression or expansion for the attack and decay portions of your sound, all without having to worry about signal levels.


Though you get four full channels of processing, the Transient Designer isn't exactly cheap, but most of the people who've heard it have been seriously impressed by the results. What it can achieve transcends by far what can be done using an ordinary compressor, in much the same way as the SPL Vitalizer takes tonal shaping beyond the conventional equaliser. The Transient Designer is most effective on drum tracks or rhythm sections — processing whole mixes is, as you might expect, often less successful, though percussive synth sounds generally respond well. Even if you record only ballads, you could still use one for polishing up your drum tracks, but as soon as you get on to dance music or anything else with a strong rhythmic element, the Transient Designer rapidly moves out of the luxury category and on to the 'must have' list. This is a unique processor that you have to hear working to appreciate, but be warned — don't play with one unless your credit card can back up what your ears are telling you!


  • Childishly easy to use.
  • Consistent results regardless of input signal level.
  • Exceptionally musical.


  • Only the price!


This is a unique dynamic processor that allows the user direct control over the feel of percussive material. The price isn't keen, but there's nothing else on the market like it.