'EQ ripping' is a technique that aims to match the frequency response of your tracks to those from CDs featuring world-class production. Of course there's a lot more to creating good music than frequency response, and unless your music is written in a similar style and with similar instrumentation such techniques can be doomed to disaster, but it can be a useful educational process if nothing else. Over the last few years several products have offered this function, including Steinberg's Free Filter and Delaydots' Spectral Shaper, but here's a new one to try.
Voxengo's Curve EQ is a 'linear phase spline equaliser' with a 2048-point filter kernel, which essentially means that you can draw highly complex responses using its graphic interface. This is very easy to use, with draggable points on an FFT display that let you alter any part of the audio spectrum over a ±30dB range. Extra points can be added by double-clicking anywhere on the graph, while existing points can be deleted in the same way, or grabbed and dragged elsewhere — a readout of the current cursor position in Hz and dB helps you pinpoint your efforts.
To the right of the FFT display is an Output level slider with a huge ±48dB range to minimise in/out level differences, and there is a cluster of somewhat anonymous buttons beneath. A Monitor button lets you view the real-time FFT response of the input or output signals, or both, for either the left or right channels, or both mixed together. Even handier is its OutAvg setting, which averages the response over 12 seconds, resetting itself after every EQ change. This option makes it far easier to judge the overall trend when examining response curves.
The buttons labelled C, M and S control the EQ ripping feature. Pressing C starts the capture process, which you can stop at any time, and once captured you can apply it to another file by using the Match button. Since the EQ difference can sometimes prove more extreme than you want if the destination file is missing some frequencies, the / and * buttons let you attenuate or amplify the response differences, and of course you can also use them as a general-purpose EQ 'gain' control for your own hand-drawn designs. The 'rst' button resets the entire response to its flat default, while Exchange and Copy let you perform A/B comparisons.
The latest version 1.5 adds 'vintage processing', with seven useful variations of odd and even harmonics to add warmth and presence to your sounds, three saturation modes to fatten them up with guitar amp/tape simulation, and even a selection of six internal filter algorithms with extremely subtle differences. However, for me the most interesting new addition was Gear Match, which lets you impose the modelled frequency-response characteristics of any two items of gear including tape, six types of tube, three varieties of compressor, and two enhancers. In combination these new features add a great deal to the package, providing a huge range of treatments ranging from subtle to extreme.
CPU overhead rose to a substantial 18 percent with stereo 44.1kHz files on my Pentium III 1GHz with all its features enabled, and like all plug-ins that analyse the incoming signal, Curve EQ also imposes a fixed delay. At 3072 samples this adds a hefty 69mS at 44.1kHz, and although this is automatically compensated when you use it on audio tracks, it sadly makes using Curve EQ rather impractical with soft synths — a version without the EQ ripping feature and optimised for real-time use would make sense. Developer Aleksey Vaneev also confirmed that it's not possible to use VST automation, since Curve EQ works with 2048-sample chunks.
Apart from these limitations, Curve EQ worked well, was easy to set up, sounded pretty good, and the 16 presets supplied show the versatility of this form of 'free-form' EQ. I managed to create some very extreme comb responses for special effects for instance, while the modelling features add punch, sparkle, and character. A range of skins is also available for download, although I would like to see a redesign and labelling of the rather anonymous buttons, particularly for the latest features.