Colectivo para la autogestión de tecnologías para la interpretación index.en.html Report on Budget Compression Options for Interpreter Audio Chains Introduction and Context At Coati’s recent work in Sri Lanka we encountered recurring problems with the sound system that directly a ff ected the interpreters. The central issue was the inconsistent levels from fl oor microphones. Since the fl oor feed was under the control of in-house technicians, we had limited redress. The result was that some speakers were so quiet that their words were lost beneath ambient noise, while others came through at painfully high levels, forcing interpreters to turn their headphone volume down. That in turn created further problems when interpreters switched to relay channels, as volume levels would be out of balance. The interpreters’ ability to work comfortably and accurately depends on a stable and predictable signal. It became clear that the cooperative needs to address these problems. The Normal Solution in Professional Setups In most professional conference and broadcast contexts, this problem is solved using rack-mounted dynamics processors These devices usually combine several functions in a single box: ▪ Compressors smooth out dynamic range by bringing up quiet passages and reducing peaks. ▪ Limiters act as a hard ceiling, protecting against sudden spikes such as mic pops, cable crackle, or shouting. This is particularly important for interpreter comfort and safety. ▪ Noise gates cut o ff the signal entirely when input falls below a set threshold, eliminating background hiss or chatter during pauses. ▪ Filters (high-pass or low-pass) allow the operator to trim out rumble, handling noise, or excessive high-frequency hiss. ▪ Noise suppression circuits address steady, narrow-band noise sources such as 50/60 Hz mains hum and its harmonics, or broad electronic hiss (they cannot remove the sound of a noisy hall or audience). The most common and compact format measures 1.75 inches (44.45 mm) high and 19-inch (482.6 mm) wide rack . A single unit typically weighs 2–3 kg, and of course a fl ight case is needed for transport. Even one or two such devices therefore add considerable bulk to the equipment Coati already has to ship or travel with. Entry-level examples of full rack units include the Behringer Composer Pro-XL MDX2600 (around €150– 170 new, dual-channel with compressor, limiter, and gate) or the DBX 266XS compressor/gate in a similar price range. For large, permanent installations, these devices are no doubt excellent, but not suitable for Coati due to their size. There are also a few mini-rack or half-rack units which shrink the form factor, often weighing under 1 kg and designed to be mounted side by side. Well-known examples are the FMR Audio RNC (Really Nice Compressor) , a respected half-rack stereo compressor costing around €200–250, or the older BOSS RCL-10 compressor/limiter/gate units from the 1980s/90s, which sometimes appear second-hand for around €75–100. These are obviously more attractive in terms of size and weight but not exactly economic, usually costing more than the full size racks. For Coati, which prioritizes portability and low weight, they are less attractive to carry to every event — hence the search for more compact and economic alternatives. Economic Alternatives Constraints around size and cost led to the consideration of potential low-cost compact alternative options. Online search pointed to a number of possibilities and three devices were purchased for appraisal: ▪ A Behringer Q502USB mixer with its single-knob compressor. This is identical to mixers we already own except for the added compressor circuit. We paid €25 but they probably cost closer to €70 new. It's worth pointing out that they include a USB sound interface so useful for hybrid setups. ▪ A Sonicake Source Comp guitar-pedal style compressor. Cost around €30-40. Parte pública Inicio Contabilidad Budget tool Presupuestos Inventario Documentos Electrónica Spider Proveedores Actas Mapa sobre la web de coati Calendario (deprecated) Coati - interno — index.en.html https://coati.pimienta.org/interno/opciones_de_compresor... 1 of 3 2/26/26, 8:15 PM ▪ A Rowin LEF-300 COMP , an ultra-budget pedal costing about €15-20. While the pedals are designed primarily for musicians rather than interpreters, the principles of compression remain the same: they reduce the di ff erence between loud and soft sounds. Unlike the rack units, they do not include limiters, noise gates, or fi lters. Other units considered but not purchased or tested include the Behringer CL-9 which is well priced at €20– 40. Method of Testing Initial tests were subjective, speaking through a microphone into each device and listening for how the signal changed as controls were varied. This wasn't especially useful for comparisons so a more systematic approach was tried. A recording was made of speech at di ff erent volume and distance from microphone, and this was then played back through each compressor using di ff erent settings while attempting to achieve a consistent desirable output. The results were captured via the Q502USB sound interface into a laptop running Audacity to compare the waveforms. This provided a visual comparison of how the dynamic range was altered by each device. Observations and Device Behaviour The Behringer mixer’s compressor is theoretically controlled as it is by just a single knob. However in practice there are three controls in play. Compression is entirely dependent on a strong input signal so the input gain on channel 1 must be turned up to just before the clipping LED is activated. Then the channel 1 output level must be increased until the status LED by the compression knob is being lit by all but the quietest of speech. This con fi guration ensures lifting the quiet moments and taming the loud peaks. The Sonicake Source Comp has lots of controls including input and output gain, a dry/wet blend, along with the traditional compressor controls - ratio, attack, release. For our purposes the dry/wet mix probably best fully to the left without blending the uncompressed signal into the mix. Like the Behringer, most of the shaping comes not from the ratio or attack/release but from correctly setting the input gain very high, then adjusting the output gain to restore overall loudness. Oddly, changes to the other controls seem to have little noticeable impact. Theoretically we want a high compression ratio, low (fast) attack, and high (slow) release. One notable advantage of this pedal is that given the controls on input and output level, the device can actually be used instead of a mixer in the context of fl oor level control. It even has su ffi cient gain to act as a microphone preamp so can replace a mixer in this context too. The Rowin compressor pedal was by far the cheapest of the three test devices and essentially has controls only for compression depth and output level. Since, like the other devices, compression only kicks in when the input level is su ffi ciently high, the lack of an input gain stage on the device itself means that unlike the Sonicake, it must be used alongside a mixer in order to provide input level control. Since Coati already has many small mixers, and always deploys one for fl oor level control, adding one of these cheap Rowin compressors is all that is required to tame levels. Comparative Analysis All three devices produced broadly similar results once enough “twiddling” was done. The distinctions are in usability and integration: ▪ The Behringer Q series mixers make most sense if we ever needed to buy new mixers anyway; the built-in compressor comes at little extra cost. ▪ The Sonicake Source Comp is the most fl exible, thanks to its input and output gain controls, and can even replace a mixer in some cases. ▪ The Rowin Blue compressor is the cheapest and simplest, entirely suitable where a mixer is already providing level control. Its missing input gain makes it less versatile than the Sonicake. Practical Considerations Each pedal uses mono jack inputs and outputs, which makes them fully compatible with our existing fl oor and transmission chains. Inputs and outputs are illustrated with arrow symbols. All of the pedal units use the standard guitar-pedal power format of 9V DC with centre-negative polarity. This is the reverse of most power supplies, including all our own 12v DC supplies, so extra care is needed to avoid accidental damage. The Sonicake unit accepts up to 18V, but still with reverse polarity. One other important limitation is that none of these devices function as true limiters. They will not block sudden pops from unplugging microphones or electrical crackle, meaning they cannot fully protect interpreters’ ears. Nor do they act as gates: with high compression, they raise background noise when no one is speaking. Gates, like limiters, are also available in pedal form and could be added if we want these features. For example, the Rowin noise gate costs about €17-20, the Behringer-NR300 costs about €22-25. An additional application for any of these compressors is at the transmission stage. Compressor/limiters are considered essential when feeding FM transmitters, as they prevent or reduce the risk of over- modulation. This is an area where these compact units could also serve Coati well, sitting between our language outputs and the FM transmitters. The Sonicakes would provide level control, removing the need to use a mixer for the task (the Rowin may be less suitable to this application). Parte pública Inicio Contabilidad Budget tool Presupuestos Inventario Documentos Electrónica Spider Proveedores Actas Mapa sobre la web de coati Calendario (deprecated) Coati - interno — index.en.html https://coati.pimienta.org/interno/opciones_de_compresor... 2 of 3 2/26/26, 8:15 PM Conclusions For Coati’s needs, compression is not optional: it is essential for interpreter comfort and for maintaining consistent, usable audio. The budget pedals tested all proved surprisingly capable, and although none are substitutes for full rack processors with limiters, gates, and fi lters, they solve the main issue we need to address. The Rowin Blue compressor stands out for its value. At €15 it makes sense for us to have one available for each of our existing mixers. The Sonicake Source Comp, while more expensive, brings fl exibility that could reduce the need for a separate mixer for fl oor level control or control of signal level to transmitters. These are the tasks we mostly use mixers for (we rarely use them as mixers) so using the Sonicake instead means less heavy bulking equipment needs to be carried. The Behringer Q series mixers are the most expensive option but are the natural choice if we ever needed to expand our mixer inventory or replace broken or lost mixers. Recommendations ▪ Consider adding a noise gate, in pedal form, to reduce background noise. ▪ Consider adding hard limiter (if compression is not su ffi cient) to protect interpreters from the loudest pops and spikes. ▪ Deploy compressor/limiters not only on incoming fl oor signals but also at FM transmission outputs, to prevent over-modulation. ▪ When purchasing new mixers, always select the Behringer Q-series with built-in compression. ▪ For standalone compression in chains that already use a mixer, the Rowin Blue compressor is the most economical and e ff ective solution. ▪ The Sonicake Source Comp is the preferred choice when we wish to control fl oor feed levels, or signals to transmitters, without also needing to deploy a mixer. ▪ Power supplies for pedal units must be clearly labeled and kept separate to avoid polarity mistakes (might even be worth modifying internally to switch polarity?). ?signal-2025-09-24-111933 002.jpeg ?signal-2025-09-24-112957 002.jpeg Parte pública Inicio Contabilidad Budget tool Presupuestos Inventario Documentos Electrónica Spider Proveedores Actas Mapa sobre la web de coati Calendario (deprecated) Coati - interno — index.en.html https://coati.pimienta.org/interno/opciones_de_compresor... 3 of 3 2/26/26, 8:15 PM