PLParEQ is a 10-band Phase-Linear Parametric Equalizer of the highest quality. Each filter may assume any of many different filter characteristics, and operate in either traditional phase-warping mode, or our phase-linear mode. It uses the same internal DSP core as all of our other high-end products. Audio streams are treated in either stereo or mono. Individual filters can be applied to either both stereo channels, middle only, or side only.

This PC VST plugin can operate in traditional 32-bit mode (24-bit audio) or as a 64-bit plugin for Cakewalks new Sonar 5. All internal processing is carried out in double-precision 64-bit floating point, regardless of external host mode.

For audio streams at sample rates below 80 kHz the DSP engine internally upsamples with high-quality Sinc interpolation, applies its filtering, and then downsamples back to your system sample rate.

Available filter types include all of the conventional resonant 2-pole lowpass, highpass, bandpass, band-reject, all-pass, high and low shelving, and the three Oxford variants of peaking/dipping filters. Also included are 1-pole lowpass and highpass, 4-pole resonant Butterworth lowpass and highpass, 6-pole notch for killing 50/60 Hz and other troublesome spurs (very tight and narrow), 1/F pinking filter, tunable 1/F lowpass (-3 dB/octave), tunable F-highpass (+3 dB/octave), and A, B, and C weighting filters. The list of filters continues to grow as we identify more useful variations.

You can run all of the filters at native sample rates higher than 80 kHz, and forego the internal upsampling conversions. Upper limits on the sample rate (> 96 kHz) are dicted primarily by your computer's capacity, and your need for high quality at the very lowest frequencies (below 100 Hz).

Individual filters can be operated as either traditional phase-warping, or phase-linear. Our algorithms employ blocked processing for phase -linear operation, and produce phase linearity by sending the signal through each filter twice - once in the forward time direction, and then again the the time reversed direction, thereby unwinding the phase back to zero.

The blocks are reassembled using very high-quality windowing and 8-fold temporal overlap. IMD resulting from phase-linear operation has been measured as -120 dB from peak signal levels. (IMD test measurements*) Corner frequencies for filters can be adjusted from 10 Hz to 30 kHz at
all sample rates

Computation proceeds in double-precision floating point throughout the entire DSP core, which uses 56-bit mantissas and 80-bit intermediate products and sums. At the last stage of conversion back to 24-bit audio, we dither with a carefully crafted white-Gaussian dither from the 56-bit mantissas to the 24-bit mantissas utilized thorughout by VST hosts. Our noise floor is typically measured at around -180 dB/Root(Hz). The Gaussian dither distribution is provably more preserving than more commonly used triangular distributions.

Our tests indicate that PLParEQ requires about 5-6% of our computer speed capacity, with each additional filter enabled requiring an additional 0.5-1% at the highest quality levels. These tests were performed on a 3 GHz Pentium-4 computer with HyperThreading enabled. Different VST hosts will show varying requirements. Our tests were performed with Mackie's Tracktion 2 as the VST host. Performance on a more modern Pentium IV are likely to show improvements upon these results.

*(IMD test measurement statistics - The signal was a -0.5 dBFS 1 kHz sinewave at 44.1 kHz SR. The filtering was performed as a Q=20 phase -linear bandpass filter centered at 1 kHz with unity gain, and using the highest quality setting = largest resampling blocksize.

The test chart exhibits a spectral resolution of 0.67 Hz, with the IMD spurs spaced by 43.1 Hz. The signal was internally upsampled to 88.2 kHz for filter application, then downsampled back to 44.1 kHz for final output.)