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Chapter 9: Compressing For A Reason

AUDIO FILES (To download all WAV examples at once: 42MB ZIP)

  • Effects Of Different Compressor Time Settings On Drums: These audio examples support Figure 9.9 in the book by demonstrating the audible effects of different attack-time and release-time settings on a snare-drum sound. The first file contains an unprocessed snare-drum sample (Ex09.01:WAV/MP3 bp). This file (Ex09.02:WAV/MP3 bp) demonstrates what the snare sounds like when processed at a ratio of 20:1 with fast attack and fast release times. Because the compressor reduces and resets the gain so quickly, the result is that the initial percussive transient is dipped in relation to the sound of the drum as a whole. The next file (Ex09.03:WAV/MP3 bp) uses the same fast-attack 20:1-ratio compression, but with a longer release time so that the gain reduction resets negligibly during the drum hit. This means that all the compressor really does is reduce the level of the whole drum hit, rather than significantly affecting the hit's character, and were there any volume differences between the hits the compression would serve to even out this irregularity. If I now also increase the attack time to around 30ms, a small section of the initial percussive transient can sneak past the compressor before it has the chance to react, as you can hear in this file (Ex09.04:WAV/MP3 bp). The end result is that the drum's sustain tail is reduced in level relative to its transient.

  • Potentially Undesirable Side-effects Of Compressor Time Settings: Attack and release times which are too short can cause problems with bass instruments, because they track the slow-moving audio waveform, introducing potentially unwanted distortion. For example, in this file (Ex09.05:WAV/MP3 bp) I've compressed the bass guitar fairly firmly at a 4:1, starting off with attack and release time settings of 0.3ms and 70ms respectively. As the file progresses, the time settings gradually shorten to end up at 1 microsecond and 1ms respectively. As this occurs, you can first hear the attack of each bass note being dulled, and then distortion creeping in as the compressor begins tracking the individual waveform excursions. Another side-effect of inappropriate compressor time settings can be a loss of low end on low-frequency percussion such as kick drums. Take this drum sample, for instance (Ex09.06:WAV/MP3 bp). If I now compress that drum with a ratio of 20:1, using a 20ms attack time and an even faster release, you can hear how the sound's low-frequency weight suffers (Ex09.07:WAV/MP3 bp).

  • Parallel Compression: Parallel compression can be very effective for emphasising sustain without destroying transients and dynamic performance nuances. As such it can be very effective for drums, as in these two examples: Example 1 uncompressed (Ex09.08:WAV/MP3 bp) and compressed (Ex09.09:WAV/MP3 bp); Example 2 uncompressed (Ex09.10:WAV/MP3 bp) and compressed (Ex09.11:WAV/MP3 bp). However, although the technique is best known for drum-processing, it also works very well for other instruments which carry important transient information, such as piano, harp, and guitar. By way of illustration, here's an example of a clean electric guitar recording without any compression (Ex09.12:WAV/MP3 bp) which has then been treated to parallel compression to add warmth and sustain (Ex09.13:WAV/MP3 bp).

  • Using The Tonal Side-effects Of Compression: Different compressor designs have different tonal side-effects, although the differences between them are usually fairly subtle. For example, compare this uncompressed vocal phrase (Ex09.14:WAV/MP3 bp) with the compressed versions from three different freeware analogue-modelling plug-ins: Digital Fishphones BlockfishWindows Logo (32-bit)32-bit (Ex09.15:WAV/MP3 bp), Tin Brooke Tales TLS3127LEAWindows Logo (32-bit)32-bit (Ex09.16:WAV/MP3 bp), and Tin Brooke Tales TLS2095LAWindows Logo (32-bit)32-bit (Ex09.17:WAV/MP3 bp) -- all three were compressing roughly the same amount. Chaining several compressors together allows you to combine these different tonal characteristics. Here, for example, is another uncompressed vocal section (Ex09.18:WAV/MP3 bp), and here's the same section compressed with Fairchild 670 and Urei 1176LN compressor emulations in series (Ex09.19:WAV/MP3 bp). You can get even more creative by running the processors in parallel instead, as in the following example: this section of uncompressed vocal (Ex09.20:WAV/MP3 bp) has been processed with an array of five different compressors in parallel to generate this file (Ex09.21:WAV/MP3 bp). Notice how the parallel approach has not only significantly altered the tone, but has also very effectively contained the dynamic range.

  • Vocal Balancing: Here's a real-world demonstration of the roles of compression and level automation when setting the vocal balance in a mix. First of all, listen to this section of my full mix (Ex09.22:WAV/MP3 bp) for this Mix Rescue project. Now compare that with this version (Ex09.23:WAV/MP3 bp), where I've bypassed the level automation. Although there's still an enormous amount of compression being applied to the vocal, it's not as consistently upfront-sounding, because the processing just isn't intelligent enough to judge how audible the vocal needs to be within the context of the mix. If I switch out the compression too (Ex09.24:WAV/MP3 bp) you can hear how the vocal struggles to hold a consistent place in the mix -- for example, given the lyric 'Heading for the rock stop at the front gate because I'm banned from the rock show', you can hear how syllables such as '-ing', 'the front', and 'be-' in particular are getting lost, which compromises the comprehensibility of the lyrics.



  • How To Use Classic Compressors: Many small-studio owners have access to a variety of digital emulations of classic analogue compressor designs. But which emulations are best suited to which musical applications? This article provides some useful pointers.

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