Compression Study #4 – Urei 1176LN GR Curves

One of the many key characteristics that gives a compressor it’s sound is the shape of the envelope in which gain reduction is applied and retracted. The attack and release parameters will affect the overall time for gain reduction to take full effect, but the curve is inherent to the compressor. This curve is how the compressor throws the energy back after squashing the signal and can alter the sound drastically.

…Some plug-in compressors have a linear mode, that applies gain reduction at a constant rate. This can be effective at adding smooth sustain to a mellow bass part, for example. But generally a linear attack and release lacks excitement and certainly doesn’t add energy to tracks, like the 1176 is known for… 

One of the reasons the 1176 is favoured by many engineers, is its ability to perform well on pretty much any instrument. This is because it is a program dependant compressor, which means the attack, release and ratio alter depending on input material.

“The 1176 will faithfully compress or limit at the selected ratio for transients, but the ratio will always increase a bit after the transient. To what degree is once again material dependent. This is true for any of the 1176’s ratio settings, and is part of the 1176’s sound” (Shanks, 2003)

Gain Reduction Curve Tests

In the following tests I have analysed how the 1176 reacts to a transient sine burst, then a sustained burst in order to capture it’s program dependant gain reduction curve. This test has been carried out at 20Hz, 100Hz, 1kHz and 5kHz to test how the compressor reacts at different frequencies. The first tests were carried out at a ratio of 4:1 with the Attack and Release set to 7 (fastest).

20Hz Burst: This first burst doesn’t tell us much about the actual GR curve, as the wavelength of the 20Hz sine wave doesn’t create a high enough resolution graph to correctly judge how GR is being applied. What this does show us however, is that the 1176 FET has a fast enough attack and release to begin wave-shaping. This can be seen in the release phases of both bursts.
Urei 1176 20Hz A7 Rl7 Rt4

100Hz: At this frequency the gain reduction curve is much more visible, Mostly on the sustained bust attack phase. At 100Hz a low frequency waveform is visible within the signal, triggering upon gain reduction enabling and disabling. This could be the mains power frequency affecting the signal as the audio voltage is directed through the gain reduction circuit. This is also visible in the 20Hz audio, upon further inspection.
Urei 1176 100Hz A7 Rl7 Rt4

1kHz: This graph is an excellent illustration of the program dependent nature of the 1176’s attack and release time/shape. After the transient burst the release throws back the gain in a steep scoop, lasting just over 200ms. Whereas the sustained burst releases more linearly before slowly scooping slightly towards the end of the release, lasting around 1400ms.  
Urei 1176 1kHz A7 Rl7 Rt4

5kHz: The initial transient attack and release resemble that of the 1kHz burst in shape, except the release appears faster, at around 100ms. Interestingly the release of the sustained burst is a completely different shape to 1kHz. At 5kHz the gain reduction releases in an arc, rather than the slight scoop at 1kHz. The release also occurs faster, at 850ms.
Urei 1176 5kHz A7 Rl7 Rt4

I imagine this type of release in the highs would create a much more transparent and ‘airy’ feel by pushing the gain up and over, whereas the scoop in the lower frequencies throws the gain back to create power. 

Full resolution images can be found here

Later in this study I will experiment with audio examples to demonstrate the effect of different compression curves, based on the findings of these bursts.


References:

Moore, A. (2012). All Buttons In: An investigation into the use of the 1176 FET compressor in popular music production. Arpjournal. [Online]. Available at: http://arpjournal.com/all-buttons-in-an-investigation-into-the-use-of-the-1176-fet-compressor-in-popular-music-production/ [Accessed: 2 February 2016].

Shanks, W. (2003). Compression Obsession: “All Buttons Mode”. Universal Audio. [Online]. Available at: http://www.uaudio.com/webzine/2003/april/index4.html [Accessed: 3 February 2016].

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