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SPL Channel One

Valve Voice Channel By Paul White
Published November 2000

SPL Channel One

Paul White might have more voice channels than he can find voices, but after using the new SPL Channel One, he gets the overwhelming urge to add another one to his armoury.

Best known for their Vitalizer range of products, SPL have also produced some pretty innovative compressors and equalisers. Furthermore, the company have a reputation not only for designing equipment that performs well, but also for taking an unconventional approach if they feel it will help them do a better job. In the all‑analogue Channel One, they've combined elements from right across their product range to create a well‑specified input channel which offers more than just the usual combination of mic amp, compression and EQ.

The styling of the Channel One follows that of previous high‑end SPL units and is distinguished by a gold front panel with an oval ventilation grille in front of the resident valve. This is a full‑voltage, dual triode used to add a little warmth and magic to the input stage, a technique that SPL have used before with considerable success in their tube Vitalizer. Each functional element of the unit enjoys its own clearly segregated section of front panel, and despite the wealth of features, the control layout is simple and largely intuitive. Each processing section has its own bypass button, while a clear bar‑graph metering system shows both the output PPM level and the amount of compressor/gate gain reduction. There are also LEDs that show the presence of signal, de‑esser activity, output clipping, and whether the valve is still warming up.

The technical spec is impressive, with a frequency response just 3dB down at 10Hz and 100kHz and a quoted dynamic range of 118dB. The signal path starts out with a hybrid tube/solid‑state preamplifier for mic, line or instrument signals — there is a high‑impedance quarter‑inch jack socket on the front panel for the last of these, and rear‑panel balanced TRS jack and XLR connections for the other signals. A button selects between mic and line/instrument modes, and both the mic and line inputs have separate gain controls.

An optional 24‑bit/96kHz A‑D/D‑A converter is available as a user‑installable upgrade, though the pricing and exact specification for this have yet to be finalised — it wasn't fitted to the review model so I couldn't check it out. An external balanced jack socket below where the blanking panel is currently fitted will feed this converter directly. Another option is that you can have high‑quality Lundahl transformers fitted to both the input and output stages.

Production Line‑up

The rear panel of the Channel One, showing the blanking panel into which an optional 24‑bit/96kHz A‑D/D‑A converter can be fitted.The rear panel of the Channel One, showing the blanking panel into which an optional 24‑bit/96kHz A‑D/D‑A converter can be fitted.

The input stage features the usual 48V phantom power, pad, low‑cut filter and phase reverse switches, and is followed by a de‑esser based around the same 'single‑knob' circuitry as the dedicated SPL model 9629 dual‑channel de‑esser, though it doesn't feature the same male/female switching. The cleverness of the design means that it doesn't need a threshold control — the side‑chain circuitry automatically tracks both the overall signal level and the sibilance level, enabling it to derive a dynamically varying de‑esser threshold without any assistance from the user. All you need to do is switch the de‑esser section on, then adjust the amount of de‑essing required using the control knob. When de‑essing takes place, only the sibilant part of the audio spectrum is notched out, so you don't suffer that annoying lisping effect that usually occurs when de‑essing is done using a full‑band compressor with an equaliser in the sidechain.

Following on from the de‑esser is a button which activates the rear‑panel balanced insert connections, allowing you to place another processor into the signal path. After the insert point is the dynamics processing: a compressor/limiter and a noise gate. As with the de‑esser, the compressor has far fewer controls than you might normally expect. There's just a single control for compression amount, a further knob for make‑up gain and a separate rotary control to set the gate threshold.

The circuitry is derived from SPL's double‑VCA drive system and is designed to cancel out any residual distortion components. Both compressor and gate have automatically adjusted time constants, and in the case of the gate this avoids clicking as the gate opens and closes. The Compression knob sets the amount of compression and combines the functions of the more common threshold and ratio controls. It appears that peak signals are processed more assertively than lower level signals, which helps keep levels under control without making the audio sound too processed. There's also a separate button that increases the compression ratio in order to deal firmly with peaks — with limiting engaged, the Compression control acts as the limiter threshold control.

Something In The Air

The compressor feeds into a three‑band equaliser section based on a variation of the circuitry developed for the Optimizer. This is adapted specifically for use with vocals and acoustic instruments, and can be switched to act before or after the compressor. The Low and Mid‑Hi controls provide both frequency and gain control, where the LF range is ±12dB and the MF range is ±14dB. The frequency ranges are 30Hz to 720Hz and 650Hz to 13.7kHz respectively, with detented controls. The high end is covered by a single Air control providing just 10dB of cut or boost for a low‑resonance high‑frequency filter. Also in this section is a variable distortion control for those who need a touch of artificial fattening and warming.

The output stage incorporates a headphone feed to allow performers using computer‑based workstations to monitor without latency. To this end, a stereo output can be fed from your soundcard into a pair of dedicated rear‑panel monitoring inputs and the level of this signal in the headphones is controlled by a separate Playback knob in the master section. A phones level control sets the overall monitoring level.

Sound & Performance

What really surprised me about this unit was how quickly I could set it up to produce a vocal sound that was significantly better than just using a straight mic amp. For example, the de‑esser is pure magic — just sing while increasing the de‑ess knob settings until the sibilance goes away. This is virtually side‑effect free, even at very high de‑ess settings, and is a significant improvement on simple compressor‑based processes.

The compressor section is just as easy to use — increase the compression setting until the gain reduction meter (or your ears) tells you the amount is right. The sound gets bigger and more even, but it doesn't pump, lose top end or go limp, as it can with some other compressors. If noise is a problem, the single‑control gate deals with it smoothly and unambiguously. If you feel you need limiting, hit the Limiter button. Most times you won't hear this working but, as it's a fairly gentle limiter, it can't guarantee that absolutely every peak will be prevented from clipping your soundcard's inputs — however, it should be fast enough to ensure that periods of clipping are too short to be noticeable. A tweak on the make‑up gain knob gets the output level back into the right ball‑park and it's time to move along to the EQ.

The star of the EQ section is, well... all of it, really! The Air control adds that expensive, breathy top end without messing up the rest of the tonal balance, while the distortion control used in the first half of its travel brings in a very convincing tube‑style warmth that thickens vocals very effectively without sounding false or overdone. It can be excessive if you push it too far, but at least there is enough range for a little creative abuse if you need it. Adding a little low end at around 80Hz gives you that intimate midnight DJ sound while the mid control is good for dealing with problem frequency areas.

I have absolutely no complaints about either the sound quality or ease of use of the processing sections, while the mic amp is as good as anything I've tried in the upper mid‑price sector. The master section features a clear, very powerful headphone amp, and the ability to monitor a computer output makes it oh‑so‑easy to add vocals to a recording without having to worry about repatching your main monitoring system because of latency.

All For One And One For All

There are cheaper front ends on the market, but the SPL Channel One excels in combining an inherently 'right' sound with a user interface that's almost too simple to allow you to get a bad result. The zero‑latency monitoring system is just icing on the cake. Until you've tried something that works this well, the words 'smooth' and 'detailed' won't have nearly as much meaning as after playing with the Channel One. If you're wondering where that elusive 'produced' vocal sound is hiding, look no further — it's in here!


  • Almost embarrassingly easy to use!
  • Sounds smooth, fat and expensive.
  • Includes an effective monitoring feature for soundcard users.


  • Using the limiter doesn't guarantee that you'll never clip the output.


Just occasionally, I try out a box that has the "I must posses it!" factor and the Channel One qualifies as such a processor.