Making eq curves with Spline EQ is really simple and fast. You have a large x-y plot with frequency on x axis and gain on y axis. On the background there is a quite unorthodox spectrum analyzer. it doesn't show Fourier transform of incoming sound nor shows spectrogram, but it uses a different approach. It shows you frequency bands as vertical bars (using the x axis reference). This bars become brighter as more energy is detected in their frequency range, they become darker and disappear when low energy or no energy is detected in their frequency range. You can watch simultaneously the unaltered spectrum (below the eq curve) and the spectrum altered by the eq (above the eq curve).
The overall graphic effect is very pleasing. To draw your curve you simply enter a number of frequency centers (yellow spots, created double clicking on the desired frequency position) and drag them to set the gain at that frequency. On the sides of the yellow spots a blue and a red one are there to define the slope of the curve.
You can also control frequency, gain, slope by three knobs on the right.
As all linear phase eq, Spline EQ introduces some latency, that's clearly reported on the GUI. A knob called precision lets you set how many filters will be active. At lower resolutions the eq cannot always match the curve you draw, so it lets you see the real eq curve in form of a dashed line. Clearly latency issues grow with higher precision values.
Spline EQ in action
The gain possibilities are amazing. I never saw anything like that. Each point can have a gain varying between - infinity to +60 dB. It is that you can completely mute some frequencies and highly enhance others. I tried Splne Eq on all kind of sonic material: overall mix (where liner phase eq tend to be used the most), but also drums, male voice, female voice, guitar, synths, strings and I have to say that it really does a good job.
Nonetheless I feel that SPLINEEQ strength lies in some more unorthodox use of its enormous power where it can really stand out
1. You can easily use it to extract or mute single instruments out of complete mixes,
due to the very very extended gain. Obviously it works best with instruments that have a quite narrow frequency spectrum. In a complete mix I was able to extract without many problems the kick drum, the bass, the cymbals and some midrange synths.
2. You can apply juicy frequency sweeps
There's a knob called "transpose" that, when moved, shifts all the curve to the left or to the right. Given the fact that almost any parameter can be automated I found myself drawing a "transpose" automation for a synth applying a very complex curve (that I would have never been able to create with the synth's internal filters).
3. You can easily cut away fixed frequency noise
I tried with some hum noise that I could easily cut without altering too much the other frequencies. the same applies for hiss.
4. You can create mind blowing, never heard effects
As I said almost any parameter in Spline EQ can be automated, so I tried to make some "extreme", experimental automation on vocal lines. The result was quite good. I could easily create wobbe effects, telephone like FX, and morph between them.
Obviously, due to latency, these tasks have to be programmed. Real time automation works fine only at lower resolutions.
CPU usage is very very low, expecially when thinking that this EQ is linear phase.
So the keyword in Spline EQ, in my opinion is POWER. While it can do a good job at subtle enhancements or at muddiness removal and at all standard uses, it really shines when used at full power, in more creative and unorthodox ways.
I think this is a very good plugin and, at 19 $, it's a REAL STEAL!