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Studio audio compressor1/14/2024 Personally, I favour VU meters (see figure 4) as the motion seems to make anticipation easier, resulting in quicker balancing of signals. Output level is probably the most useful meter to follow whilst tuning a compressor. However, your ears should give the first indication as to whether the amount of compression is too much. The compression level will give you an idea of how much compression is being applied when the result is less audible. This is the same for any dynamics processor after tuning, input level should become the most dramatic control parameter. It is important to check input level and maintain it after setting a compressor as any adjustment made to the input level will change the entire response of the compressor. Usually there will be three display modes: Input level, compression and output level. This can be used to gently level out sustained sounds such as vocals.Īlong with these two meter modes, one should also pay attention to what kind of information the compressor’s meter is reporting. This form of metering is important when treating transient sounds.Īverage, RMS level, can be used to achieve a smoother response from a compressor whilst it gradually adjusts over time. Peak level will have more dynamic range as it relates to the peaks and troughs of an audio signal, which can be viewed as part of its waveform in an audio editor. Whilst this is logical, there are two metering methods which dynamically influence response: Peak, which follows peak level and RMS metering, which follows an approximate average level. It is important to note that how the compressor measures incoming signals will impact on performance and sound results. The green “knee” is the transition point above the threshold. As the black line of amplitude rises above the red threshold line, we observe the results of the ratio being increased in blue as overshoot is reduced. This is the essence of dynamic range compression: The signal is attenuated towards the threshold based the proportions of the ratio (see figures 2 and 3).įigure 3: A graph depicting compression causing deviation from linear amplitude. With a threshold of -3dB, our output would measure around -1dB. Therefore, if our input signal is +8dB over the threshold and our ratio is 4:1, we will measure this signal as +2dB over the threshold. However, different ratios, such as 2:1, implies that two decibels over the threshold will be required to equal one decibel out. This is quite simple to understand: A ratio of 1:1 is equal – if the signal exceeds the threshold, no attenuation will take place you put one in and get one out in. The dotted line denotes an unheard/side-chained control signal.Īs the signal rises above the threshold, gain is reduced in accordance to a ratio. Either the main input or side-chain/key input is read by an envelope follower, which is then used to trigger compression. The most common application for a compressor is as a channel insert effect, where the compressor will be used to measure the input signal and apply gain changes based on its relativity to a preset threshold.įigure 2: Signal flow diagram of a basic compressor. This reduces the dynamic range of a signal and, in turn, increases RMS (root mean squared) level contributing to perceived loudness. Ignoring control parameters for one moment, the operative feature of an audio compressor is to attenuate gain based on the level of an input signal. Knowledge and techniques presented here can be applied to both hardware and software compressors (see figure 1).įigure 1: The UAD LA 2A above and a software emulation below. This paper does not discuss upwards compression or expanders, though the principals should be easily understood after reading the following pages. This paper is intended for beginners as it provides a basic overview of how a compressor works lists several uses for compression to help understand which problems it can fix gives practical advice for tuning compressors by ear and with meters and concludes with a handful of less obvious tricks. I have been using compressors for over a decade now and whilst my approach remains similar, I have noticed a growing appreciation for the tonal control they offer. A reference table is provided as a guide towards using compressors to glean specific results.Ĭompression tends to take a lot of experience to fully understand. This paper provides a complete overview of and uses for dynamic range audio compression.
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