Another problem may occur while using fast release times on low-frequency sounds.
Reducing the release time should ensure that the compressor threshold does not pump between the long, low-frequency cycles, or unduly affect the end of the sound envelope.
When recording an acoustic bass, many of the above problems are exacerbated by the instrument’s acoustical characteristics and the recording environment.
Synthesizer bass can also create significant level problems, some of which can be reduced by using low compression ratios.
For shorter, sequenced bass synth sounds, a large amount of compression followed by heavy expansion at a high ratio forces the sound envelope to push its way through the noise gate, thereby creating a tight, expanding sound.
Synthesizers seem to need a certain amount of compression, because no longer are you dealing with a natural sound that must be treated carefully to retain certain inherent sonic qualities. In many cases, radical processing may help make the sound more real.
Synthesized horns parts, for example, can often be greatly enhanced by RMS compression at ratios between 1.5:1 and 4:1, and compression from 5dB to 8dB or more, depending on the characteristics of the patch and compressor being used. A thicker, punchier and more dense sound can be achieved as the compressor positively affects the synthesis overtones, by squashing them together. Percussive synthesizer sounds often contain jagged and irregular peaks that can be controlled various ways.
For level control, use higher limiting ratios (8:1 or greater) on a peak device, or the peak setting on switchable unit, to control excessive level swings without affecting the lower-level program material.
Another approach is to compress the sound at low ratios to reduce both high and low-level program levels. Again, this technique depends on the sound being created, because you are dealing with synthetic sounds.
With samplers and sampling keyboards, particularly 16 -bit devices, the question of what’s real may become a moot point when sound quality is compared to the analog recording process. The latter’s inherent weaknesses and compensations include pre-emphasis, de-emphasis, NAB and AES equalization, record and playback head gap loss, and so on. So, when dealing with high-end sampling technology, some caution must be used to retain the “natural” sound, whatever that may mean today.
The electric guitar seems to enjoy compression for many effects. When close-micing a loud rock-and-roll guitar amp, squashing the sound at low compression ratios with a slow release time adds sustain, and definitely makes it easier to place in a mix. Another trick is to heavily compress the ambient mics by between 6dB and 10dB, thereby creating a denser, sustained ambience.
Although heavy compression makes it easier to place a raucous guitar in a complex track, it can have the negative effect of making the overall sound appear smaller. As a result, compression should be approached with care, or avoided, when recording a power-rock trio where the guitar is the only chordal instrument.
When recording direct or close-miced chordal guitars, high compression with correct equalization can create a brilliant, shimmering sound with little or no attack. The sound appears to swell after the strum because of the pumping action of the compressor’s release.
To help keep lead guitar solos highly audible, to add sustain and to avoid level problems during mixdown, compression may be used to compensate for vast level swings between guitar notes. Such level problems may be caused by a variety of factors, including the guitar’s fretboard design; the tubes in the guitar amp, which may feature different harmonic frequencies; or the musician’s pick attack during the solo, which may send differing amounts of voltage from the pickup.
For R&B style, single-note picking, a slow attack time will allow through the percussive attack before compression begins, and a quick release will pop the level back up between notes, creating the “percolator” effect. When played as a solo instrument, the acoustic guitar usually requires no limiting or compression.
Unfortunately, in order to fit a plucked or picked steel string into today’s complex mixes, something has to give, and it’s usually the guitar’s natural fidelity. This is not always bad; many of today’s most popular steel string sounds are highly compressed. An example is the popular rock/pop strummed sound that features the string sound over the instrument’s resonance.
The gut string guitar is another instrument that sounds much better in its natural form than when it’s been compressed or limited. For placement in a pop mix, however, it is usually necessary to reduce the dynamic range. Experimentation is the only solution.