(Image Top-Bottom: Gain, Frequency, Q, In/Out Type)
Gain may be adjusted in the range +18.0 to -18.0dB, in increments of 0.1dB via the #Gain Value Windows or by ‘dragging’ the EQ curve. The displayed frequency response graph shows a range of +/- 18.0dB.
The #Frequency control displays the center frequency for each band when a bell filter is selected. When in cut or shelf modes, the Freq parameter controls the corner frequency of the filter.
The Frequency control values are adjustable in one-sixteenth-tone steps (96 steps per octave), rounded to the closest integer. The left/right arrow keys may be used to step the selected Freq value in one-sixteenth- tone increments.
The Q control displays the Q value, which functions differently for each filter type.
• Bell - Q corresponds to the width of the frequency range for that band.
• Shelf - Q controls the slope of the “side” of the shelf and the resonant dips and peaks.
• Cut - (bands 1 or 6 only), Q controls the slope of the cut filter (from about 10dB/oct to 18dB/oct), plus controls the “bump” in the slope, as explained in the previous chapter.
In all cases, when Q is a higher value (bigger number) the slopes of all filters are generally steeper; bells are narrower, cut and shelf filters are more sharply sloped.
More about Q
Q is a way of expressing the frequency width of a filter in relation to the center frequency of the filter band and may be represented by the mathematical relationship: Fc/Fw (center frequency divided by frequency width at the traditional ‘-3dB point’, both in Hertz). For example, a Q of 2.0 at 1,000Hz gives a bandwidth of 500Hz (1000Hz divided by 2).
In the Renaissance Equalizer, the Q value is the traditional “engineering Q” for the bell filters, but only for positive gain. When used as a negative gain, the filter’s asymmetrical property, described in the previous chapter, is actually narrower than an equalizer with symmetrical behavior. Therefore, a #REQ bell filter with negative gain sounds sharper; it would be equivalent to a higher #Q on a symmetrical bell equalizer, roughly double the Q of its value.
At the bottom of the controls is a row of dual-toggle buttons. Each has two toggles; one to switch each band In or Out, and one to control the Filter Type. Please recall that not all bands have the same complement of filter types.
Bands 1 and 6 have cuts, bells, and shelves. Bands 2 and 3 have bells and low shelves; bands 4 and 5 have bells and high shelves.
Click the #Filter Type button to toggle through the available selections for that band. On some platforms, you can option-click the Filter Type buttons to display a popup for direct selection; not all programs support popups in plug-in windoids, so the toggle mode is the default method of selecting the filter.
Each filter curve is represented by an icon, shown here from left to right.
To switch the band In or Out, click the left edge of the control; when the band is In, the control will illuminate with the corresponding color of the band marker.
One special feature of 48-bit processing is the ability to use some headroom to completely avoid internal clipping. The REQ automatically eliminates any clipping in each band (which could occur in the Q10 and other equalizers). Such clips would not be indicated on input or output meters, but would certainly affect the signal.
Because of this feature in REQ, input gain controls are unnecessary; only an output gain control is needed, as it is certainly possible to clip the output by boosting the EQ of an already-hot signal. Fortunately, the same headroom allows the REQ to calculate exactly how far “over” a signal goes beyond 0dBFS (full scale digital).
In the center area just above the meters is the #Trim button, calibrated in dB. Just below it is the clip light, shown illuminated here; the Trim button indicates a signal 3.1dB below full-scale. The positive value of the number indicates that there is still some headroom available, although we’re close to full-scale (0dB FS)..
If there was headroom, the value is positive (and the clip light is not illuminated), which shows the faders can be moved upward 3.1dB without any clipping. This is sometimes called “margin” on some processors and recorders and simply shows how close the signal came has come to 0.0dBFS (full scale digital).
To Trim the faders, simply click the Trim button once to automatically move the faders by the value shown in the button. When you do so, Trim will reset to “12.0”, the maximum positive gain allowed (for reasonable safety in such matters).
To reset the Trim (and the meters) without changing the faders’ values, click anywhere in the meters or between them. If you accidentally click the Trim.
In this illustration,
the signal has #clipped (as shown by the red clip light) and needs to be reduced 3.9dB (so the negative sign indicates which way the level must go). If clicking directly on the number (-3.8) will Trim the faders by the amount indicated; here, the faders will be reduced by 3.8 dB, to avoid clipping.
Types of EQ Filters (Cut and Bell Filters)
What the filters are:
You might be wondering what “resonant #shelves” are, or if you’ve already been using the Renaissance EQ and are just now reading this sentence, you might be doing so to find out just what a #Gerzon Shelf or a #Baxandall filter really is.
Resonant shelf filters
Michael Gerzon proposed the idea of a resonant shelf in a confidential paper to #Waves in 1994. Analog filters (specifically, Pultec) had already achieved this type of EQ behavior by using both the cut and boost knobs simultaneously. Mr. Gerzon had defined a way to make this acoustically-desirable behavior into a single filter type. He did not live to see the implementation of his proposal. We have named some of the presets using these shelves in his honor although our implementation is not quite exactly his proposal. Instead, they are a compromise between his idea and the great sound of the Pultec filters, with thanks to suggestions from Craig “Hutch” Hutchinson.
Types of Filters:
Again, a variable Q value makes these cut filters distinctively different from typical cut filters. The Q changes the slope of the line, plus includes a bump in the frequency response that allows the filter to be more musical and pleasing, while still performing the basic operation of a cut filter: to “clean up” unwanted frequencies outside of a given range.
Initially, it might seem that using a sharp filter would be the best thing to really remove unwanted frequencies. However, if a very sharp brick wall filter is employed to cut off these frequencies, there is a psychoacoustic effect of making the sound very dull (when using a high cut). By allowing a few of these frequencies to remain, the removal of frequencies is performed and the resulting #sound is sweeter and not as dull. Please note that this situation is not applicable to multimedia or other bandlimited requirements such as various digital conversions, which do require very sharp brick wall filtering.
Bands 1 and 6 are #third-order filters (equal to 18dB/octave). When the Q=1.0, then they are indeed 18dB/octave, without the bump. As seen below:
In order to show the bump of a higher Q value, which is below the edge of the graph of the REQ, here is a screenshot of the Waves PAZ real-time analyzer. It was created by a sine-wave frequency sweep of a high cut filter at 2kHz, with a Q=1.41:
When the value of Q is higher than 1.0, the notch and bump actually give a higher slope than a 3rd order filter, but still allow some of the higher harmonics to pass thru, although greatly reduced.
When the value of Q is at its smallest (0.71), the slope is slightly less than a #2nd-order filter, about 10dB/octave:
Bell filters (parametric)
George Massenberg invented the parametric equalizer, and most people are quite accustomed to using them. Almost completely without exception, they have symmetrical response characteristics. However, when we use an equalizer to boost, it is nearly always for tonal correction, and when cutting, for removal of bothersome artifacts. The asymmetrical filters had been described by several audio researchers and designers (including Mitra, “Hutch” Hutchinson, and others), but not included in any commercial products to our knowledge; Waves chose to include this type of filter simply because it sounded better for high-end use.
What does symmetrical mean? Simply that most equalizers have exactly the same response in the boost or gain of a bell filter, seen here:
However, an asymmetrical response, is, in a way, the most “natural” thing for an equalizer to do in the analog domain. To put it in other words, for a constant value of Q, a boost and a cut at the same frequency of a bell filter will not have the same shape. Here is the same setting (engineering Q=1.0) but on the REQ:
EQ Frequently Asked Questions
Q: How can an analog equalizer be emulated in digital processing?
A: Since each equalizer, whether analog or digital, can be essentially described as a mathematical function (and indeed, the values of analog components are directly derived from such math), then it is certainly possible to simply do the same math in a digital processor. At issue is the more curious effects of analog gear, (such as extended frequency response, with some analog equalizers going all the way to 300kHz), inductor saturation, transformer characteristics, and so forth.
Q: The bell filters of the REQ are wide when the gain is positive, and narrower when gain is negative. Why?
A: In a way, this is the most ‘natural’ behavior of #analog filters. For a constant value of “Q” (width), a boost or cut will look and sound different. These types of filters are non-symmetrical, unlike the filters in the Q10 (and nearly every EQ in the world), which are symmetrical.
Q: Shelving filters of the REQ also have a different shape to them. Why?
A: Primarily because they have adjustable slope; simply change the Q to adjust the angle of the slope going to the shelf. Part of this type of filter, called a resonant shelf, is the characteristic “bump” in the graph. The overshoot/undershoot on the angle of the slope is quite important to the sound of these shelves, first available in the Pultec (by using both the cut and boost knobs simultaneously!), then later described by Michael Gerzon in a 1994 paper as a proposed digital equalizer design for Waves.
Q: What does 48bit processing really mean?
A: Renaissance Equalizer is a dual-precision processor. This means all calculations are carried out to a #48bit value within the REQ (on fixed-point #DSP chips); for native processing, it is performed with 64bit floating-point values. This preserves greater resolution of fine details, and definitely affects the sound of the equalizer. By working at this level of precision, the most exacting details are maintained throughout the processor. Only at the output does this dual-precision data path become reduced. This reduction is performed by dithering the 48bit internal data to the desired output.
Waves Renaissance Equalizer Manual