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TL Audio Ivory Series VP5051

Valve Processor By David Mellor
Published February 1998

TL Audio Ivory Series VP5051

David Mellor warms to TL Audio's new mid‑range valve voice processor.

In a well known London studio a year or so ago, an engineer I was talking to expressed a preference for certain channels of the studio's SSL mixing console for recording vocals. On the surface, all the channels looked identical. But the console was over 10 years old and apparently, over the course of time, some channels had 'mellowed' more gracefully than others. I'm sure the studio's maintenance engineer could have corrected the discrepancy and brought all the channels back to their original specifications, but that would have removed the element of choice which effectively gave the engineer more tools in his recording toolkit. Choice in voice processors is not something we're short of these days, and it won't be long before it's possible to assemble a sizable recording console — well, at least the channel section — from different voice processors!

The TL Audio Ivory series gives us another range of processors from which to choose, and is certainly very welcome. And unlike some other products, which appear to do very little and cost the earth, the Ivory range offers a lot for a much more reasonable price. You might be tempted to think that lower prices may mean inferior performance, but if the other models in the range come up to the standard of the valve voice processor reviewed here, you're in for a surprise. TL Audio have an extensive catalogue of products, with other ranges which include the Classic Valve Series, the Indigo Valve Series and the Crimson Solid State Series. There's a lot of activity going on in TL Audio's laboratories and they obviously know a thing or two about valve as well as solid‑state electronics. They even make a valve mixing console!

The VP5051

The VP5051 Valve Processor is what has come to be known as a voice channel or voice processor. Basically, it offers, in a simple package, the processes you are likely to want to use when recording vocals — amplification, compression, EQ and an expander/gate. This goes beyond the capability of the simple outboard mic preamp, of the type that some engineers use for the sake of sheer excellence of sound quality, and sometimes consistency, when travelling from studio to studio. Many engineers, indeed, prefer to record 'flat' to tape, with no effects of any kind. This is so that the recording is as pure and unadulterated as it can be, and all the processing is left to the mixing stage, when it can be judged in the context of all the other sounds in the arrangement.

If this is the way you like to work, a full voice channel would be overkill. But the combination of voice and microphone often gives a less than perfect sound, even with a good singer and a good mic. Most singers need at least a little compression to even out the dynamics of the voice. Likewise, no mic gives its best performance, technically speaking, with the singer only inches away from the diaphragm. Working close to the mic emphasises certain elements of the voice to good effect but it also changes the frequency balance, particularly with directional mics. EQ is sometimes, therefore, necessary to correct this, and also to provide the extra brightness we have become accustomed to in recordings. The aim should be to record a sound that has controlled dynamics and the right balance of frequencies. Consider this, rather than simply the raw output from the mic, as the perfect sound, that you can later bend and shape to your will at the mixing stage.

Input Options

As should be the norm in all voice processors, and mixing console channels too, the VP5051 has three input options: mic, line and instrument. As an additional option, the mic input can provide 48V phantom power. All three alternative inputs share a common gain control. Since this is a valve unit, as the gain is increased so that the signal approaches the clipping point, the distortion level gradually increases, so there's a 'Drive' LED which indicates how hard you're pushing the electrons through the glass bubble. The brighter this LED glows, the more 'valve sound' you're getting. Watch out for the clip LED, though. If you're driving the input hard, inevitably your headroom is reduced and you risk clipping, which does not sound at all pleasant. A 90Hz low‑cut filter deals with any problematic low frequencies.


The compressor section has a full set of features, with controls for Attack, Release, Threshold, Ratio and Gain Make‑Up. Surprisingly, the Attack and Release controls are both four‑position rotary switches rather than continuously variable controls. I know that valve circuits work in strange ways (I have only ever designed circuits with transistors and ICs) but I wouldn't have thought that a switch was really necessary here. (Perhaps it's a 'retro' design feature.) Having had my little moan, I must admit that there is something to be said for rotary switches, since they restrict your range of options, but not necessarily the limits of that range, and prevent you from being more finicky than will benefit the end product.

An accessory to the compressor section is a single‑knob expander/gate. As always with compressors, more compression results in more noise, since the difference between the highest and lowest levels is reduced. An expander or a gate is often useful in such a situation, but if you're expanding or gating prior to recording, it's absolutely vital that none of the signal you want is lost, since you can't get it back. This imposes very stringent requirements on any voice channel that incorporates an expander or gate, since if it didn't work absolutely correctly, that feature wouldn't be usable.


Moving on along the signal path, we find the EQ section. Some voice channels provide parametric EQ where some or all of the sections have boost/cut, frequency and Q controls (Q is the sharpness of the peak or dip in the response). Although I like to have a parametric EQ available somewhere in my rack, just in case, I'm not a great fan of having Q controls on every EQ section of every piece of equipment. If the designer chooses a good value for Q, that becomes part of the character of the EQ, and you can spend more time on the gain and frequency controls, which are more important. The two mid‑band sections of the 5051's EQ do, indeed, have a fixed Q (0.5), and I feel that's all they need. The LF and HF sections are shelving, with up to 12dB boost or cut.

Like the attack and release controls of the compressor, the EQ frequency controls are rotary switches, with centre frequencies as follows:

LF: 60Hz, 120Hz, 250Hz and 500Hz
Low Mid: 250Hz, 500Hz, 1kHz and 2.2kHz
High Mid: 1.5kHz, 2.2kHz, 3.6kHz and 5kHz
HF: 2.2kHz, 5kHz, 8kHz and 12kHz

One final point about the EQ section is that there's an EQ in/out button, as in the compression section. This is great, not just for comparing the processed and unprocessed sound, but also for shortening the signal path when the EQ isn't needed.


On the right hand side of the unit is the output and metering section. I love the VU‑style mechanical meter, not for its retro look, but because I like mechanical meters. On a unit such as this, it doesn't particularly matter that VU meters tend to under‑read transients and that there is no associated peak LED. The meter can be switched to read the input level, output level, output with 10dB boost (if you need to see what's going on at low signal levels) and gain reduction. The gain reduction position shows the degree of compression at any instant. If the signal is below the compressor's threshold level, the meter indicates 0dB. Once the signal exceeds the threshold, the meter indicates the amount by which the compressor squashes it back down. When you're using the gain reduction setting of the meter, obviously you can't at the same time check the input level. Since this unit encourages you to use outrageously high gain settings (rightly, since it is intended to exploit the characteristics of valves at high signal levels), you may find when you switch back from the gain reduction position that the needle is hitting the end stop, and very noisily too. I wouldn't call it a problem, just a little idiosyncrasy that gives the VP5051 more character!

Also in this section is a clever little button that places the EQ section before the compressor. If you're wondering why you should want to do this, suppose you had a singer with a good voice and a good mic, and the two combined well. In this case you would probably want to compress first to even out the dynamic range, and then EQ the compressed signal to enhance it further. But if the signal from the mic had a less than perfect frequency balance, it wouldn't make sense to compress it right away, because the level‑sensing element of the compressor would be basing its action on false information. In this case it is best to use the EQ before the compressor, so that the compressor is working on a good signal. In fact, it would be really nice to be able to EQ before and after the compressor, but that's a facility you're very unlikely to come across in a single unit.

The very last button on the VP5051, if I exclude the power switch, is a Link button. This is a single‑channel unit, and you may want to splash out on two so that you can process stereo signals. However, if you compress a stereo signal with independent compressors, the stereo image tends to swing back and forth, due to the different amounts of gain reduction applied to each channel. Fortunately, the VP5051's Link feature allows you to connect a cable between two units, so that you can indeed do proper stereo compression, where the gain reduction of both channels is forced to be the same. A nice touch. Another nice touch, although you can't see it from the front panel, is a side‑chain input, so that you can do frequency‑conscious compression with the aid of an additional equaliser — if you want to do de‑essing, for example.

...the VP5051 is equivalent to a decent console mic preamp, and better than some, but then it goes beyond that, giving you the ability to push the valves and obtain a warmer, more present, more intimate sound from a good mic.


This is the big one, since if the VP5051 doesn't perform better than the mic amps in your console there isn't really any point in buying it. Subjectively, I would say that the VP5051 is equivalent to a decent console mic preamp, and better than some, but then it goes beyond that, giving you the ability to push the valves and obtain a warmer, more present, more intimate sound from a good mic. It isn't an effect that is immediately obvious, but subtle and deceptively beneficial. Likewise, the compressor isn't the type that you can use to twist the signal into a contorted parody of what a human voice is supposed to sound like (which sometimes you might want to do). This compressor is gentle and easy to use in an unobtrusive manner — although putting the EQ before the compressor can allow more exaggerated effects.

The EQ section is fine for its intended purpose, and if it doesn't offer the precision you might sometimes want, due to the switched frequency controls and lack of adjustable Q, you can always EQ further when you mix. A minor doubt I had was that the switches produce a small electrical click when they are turned. There are ways and means in circuit design of preventing switches from doing this, but perhaps it's more difficult in a valve circuit.

The expander gate isn't as quite good as the very best I have heard, but it is good, and it is possible to set a threshold low enough so that the often quiet start of 'f' and 's' sounds is captured. Even at such a low threshold, the gate will still open and close reliably, if at the expense of a little waiting time before the gate closes.


Any good voice channel isn't just a voice channel, and the line and instrument inputs of the VP5051 allow it to be used in many ways. For instance, the cold, clear sound of modern synthesizers can benefit enormously from a little valve warmth, and while you're at it you might as well try out some compression and EQ, because you don't really want to use standard patches unmodified all the time, do you? You might think it's a drawback to plug one channel of a keyboard's stereo outputs into this single‑channel module and lose the stereo effect. But recording keyboards in stereo eats up tracks (to the benefit of Alesis and Tascam, no doubt!) and often ends up cluttering the mix anyway, so why not? And even at mix time, the line input of the VP5051 will prove its worth when one track stubbornly refuses to sit correctly among the other instruments and your console's EQ doesn't have quite the right facilities to bend it to your will.

This, indeed, is the kind of unit that you would find yourself using on every session and probably every mix too. The TL Audio Ivory Series VP5051 is a great sounding, well featured product at a price that offers good value. I can't wait to hear the rest of the range!

Line vs Mic Inputs

You might not be quite sure what the difference is between a line and an instrument input, both of which are present on the VP5051. Well, the line input is, to put it simply, for any source that is powered from the mains, or at least several Duracell batteries. It could be a keyboard, sampler, or one of the tracks of a multitrack recorder. They all provide a line‑level signal. An electric guitar, on the other hand, is powered only by the swipe of the plectrum and therefore can produce only a weak signal — reasonably strong in voltage, perhaps, but impoverished in current. Such an instrument needs a so‑called high‑impedance input which doesn't demand as much current as a normal line input does. The noise level is a little higher, as is the susceptibility to interference, but it retains the full brightness and attack of the instrument. Conveniently, the instrument input of the VP5051 is on the front panel, exactly where a guitarist would want to plug in his jack lead.


  • The valve sound works beautifully when driven hard.
  • Good compression and EQ.
  • Excellent feature set.
  • Fair price.


  • The EQ switches generate a slight electrical click when turned.
  • Some may see switched compression and EQ controls as a con.


The VP5051 puts voice channels in the price bracket they ought to be in. It sounds great, does the lot, and is well worth buying.


£469 including VAT.

Published February 1998