You are here

TL Audio C2021

Indigo Tube Compressor By Paul White
Published September 1996

Paul White checks out the latest addition to TL Audio's new Indigo range.

Following on from the two Indigo range tube equalisers reviewed in last month's SOS, TL Audio have now added a dual‑channel, soft‑knee tube compressor to the Indigo family. Like its siblings, the C2021 combines solid‑state and valve circuitry to improve both tone and reliability while keeping the cost acceptably low.

Quick Tour

All the Indigo processors run on mains power, rather than external adaptors, and are fitted with both unbalanced jacks and balanced XLRs to facilitate connection to both pro and semi‑pro systems. A further pair of front panel instrument jacks accept high‑impedance sources such as guitars, and these have switchable high/low sensitivity. All three inputs are active simultaneously, which means you can mix inputs, though there's no independent level control. In this particular circuit, the valve is used as the compressor gain control element, which is how the original tube compressor used to work.

A glance at the front panel reveals that the controls have been simplified by using switched fast and slow attack and release times rather than making them fully variable, but this isn't as limiting as it seems, because some degree of programme dependency has been built in to allow the compressor to adapt automatically to the dynamics of the input signal. Conventional rotary controls are provided for Gain, Threshold, Ratio and Makeup, and each of the two channels has its own Bypass switch. A Stereo Link button gangs the channel for stereo operation, and in this mode, channel A's controls affect both channels. The two bargraph meters may be switched to show either gain reduction or output level, and a TRS jack side‑chain insert point enables an equaliser to be connected for de‑essing.

In Use

In practice, the C2021 can be used to provide very mild compression, or it can be wound up to the point where it functions almost as a limiter with a 30:1 ratio. The inclusion of an input Gain control means that you can bypass the compressor, then use the output level meter to optimise the input gain setting — a good idea — after which the controls are set up in much the same way as for any other compressor. Being a valve compressor, you're probably going to be buying the C2021 for its sound rather than its outright honesty, but what I particularly like about this unit is that the sound doesn't become 'fuzzy' and 'squashed' as it tends to with some of the less well designed valve processors; the magic words 'warmth and clarity' seem apt. In addition to its first‑rate performance on vocals, the C2021 also sounds great for DI'ing clean guitar, where it thickens and adds sustain, while at the same time preserving the natural attack of the instrument.

I expected to find the switchable attack and release settings a trifle limiting, but for all routine jobs, they seem to cope fine — presumably due to the programme‑dependent element of their operation. There's also plenty of headroom, and I couldn't get the unit to clip audibly until the signal had been driven well off the end of the output level meters.


At just over £700, this is one of the more cost‑effective valve compressors, and although its feature set is fairly basic, the all‑important sound compares well with that produced by some of its more esoteric and expensive American competitors. For general applications, such as vocal, instrument or mix compression, the C2021 works very well indeed, and while it doesn't have an overtly valve sound, what it does add is subjectively constructive. In other words, you get a little warmth and thickening, but without your sound turning into some sort of audio soup; and at the top end, the sound projects well without becoming harsh or aggressive.

On balance, I think that TL Audio's hybrid approach is well engineered, and easily justified by the subjective results. I don't think it's essential to use valves to get a warm, smooth tonality, but the better FET‑based designs cost just as much the C2021, which means you might as well go the whole hog and have the real thing. The all‑important styling remains professional with just a dash of panache, and the simple operating system means that you don't get sidetracked into messing with parameters that don't really matter. While the signal processing side of the market is becoming more than a little crowded, I think the Indigo range has enough strong points to put it alongside the top contenders.


  • Smart design.
  • Sensibly priced.
  • Excellent sound quality.


  • Some users may be put off by the lack of fully variable attack and release settings.


The C2021 is a welcome addition to the Indigo range and combines easy‑to‑use compression with subtle but positive coloration.