Orange vs. Red

We investigated all thinkable theories dealing with linear-phase filters to find out the best one for our linear-phase equalizer. At the end of our extensive research and countless tests two methods seemed to be good candidates for our products. Although both lead to extraordinary clean sound and similar features, each of them has some so special, individual properties that we decided to design two independent products: LinearPhase PEQ Red and LinearPhase PEQ Orange. Some mastering engineers clearly prefer Red, some of them Orange, but also many of them use both, often even serially connected.

We frequently have been asked about the differences between the Red and the Orange. It is difficult to describe their sonic characteristics; therefore we better leave up the decision to our customers. From the technical point of view there are a few major differences:


LinearPhase PEQ Red

• LinearPhase PEQ Red works in frequency domain, i.e. the input signal is first continuously transformed to its spectral representation. Special measures have been taken to ensure high resolution for low frequencies while keeping time resolution untouched. Unlike other frequency-domain filters, this avoids drums or other instrument containing strong transients to be blurred. In addition, extremely high computing resolution has been used to avoid any cumulative truncating effects typical in complex frequency transformations. This results in untouched sound quality.
• Experts say that most of digital equalizers do not sound like their analog predecessors, especially when working with 44.1 or 48 kHz sampling frequency. Spectrum modifications in high-frequency region sound as improperly balanced. The reason is so the called frequency warping which makes the bells asymmetric and high shelving and high-cut filters much steeper as theoretically adjusted in the parameter fields. To make the filter in LinearPhase PEQ Red analog sounding we applied special corrections to the original digital filters making them look exactly like their analog reference.
  
  There are a few other PlugIns on the market using frequency-domain techniques. Most of them apply relatively low frequency resolution and claim that frequency response mathematically interpolated between a few set up points or just free-hand drawn is the best solution ever. This may be true for some industrial applications, but such filters don’t sound musically. Shapes of the filters in the LinearPhase PEQ Red exactly match the best analog references that sonic quality is indisputable, also for standard sampling frequencies: 44.1 and 48 kHz.
• LinearPhase PEQ Red features the Continuous Slope Filter technology, an Algorithmix proprietary and worldwide unique filter design. It allows extremely flexible shelving and cut filters. Low shelving (LS-CS) and high shelving (HS-CS) continuous-slope filters emulate any critically damped shelf in the range from 1^st to 4^th order including all imaginary filters in-between. Imaginary, because critically damped filters offers only slopes in 6 dB/octave steps: 6, 12, 18, 24 and so on. Our continuous-slope low/high-cut filter (LHC-CS) performs similarly. It can continuously change its slope from a critically damped 4^th order low-cut equivalent, through 3^rd, 2^nd, and 1^st order down to zero, and then turn into critically damped high-cut being a mirror of the continuous-slope low-cut at the same cut-off frequency.


Such in-between frequency-response filter characteristics, especially with slopes below 6 dB/octave (e.g. 2.2 dB/octave) are absolutely impossible to implement with classical filter technology. The only work-around way would be to cascade many 1st order filters with specially weighted amplitudes to get the overall amplitude envelope lower then 6 dB/octave (a typical example for this is the analog pink-noise filter). Such cascaded filter, however, deliver quite wavy frequency-response characteristic and are tainted with phase-shift. In opposite, the LHC-CS filter from Algorithmix allow very gentle and smooth spectrum changes without any phase shift.
• In general, the LinearPhase PEQ Red sounds a bit softer than its brother, the LinearPhase PEQ Orange. Its extremely flexible shelving filters are particularly popular for gentle brightening (highs) and enlarging (lows) effects in dense mixes, especially if traditional PEQs fail. For subjective opinions about experiences with both Red and Orange  click on the respective menu point “Client Testimonials” and read what our customers say.

LinearPhase PEQ Orange

• LinearPhase PEQ Orange works in time domain using proprietary filter technology. It is not based on FIR filters because these have some known problems like bad resolution for low frequencies, difficulties in emulating shapes of musical sounding filters, a lot of efforts for seamless parameter update, and relatively high noise floor when keeping the filter reasonably short. We rather use a special kind of normally non-causal forward/backward filter which have been respectively modified to be causal. An extremely high computing resolution is used to achieve a filter dynamic below the hearing threshold and thus crystal clear sound.
• Like already mentioned above for the Red, experts say that most of digital equalizers do not sound like their analog predecessors, especially when working with 44.1 or 48 kHz sampling frequency. Spectrum modifications in the high-frequency region sound as improperly balanced. The reason is the so called frequency warping which makes the bells asymmetric and high shelving and high-cut filters much steeper as theoretically adjusted in the parameter fields. With some experience this problem can be partly compensated by a parameter re-adjustment, however, the bell asymmetry cannot be avoided this way.
  
  To make the filter automatically sound more analog for 44.1 and 48 kHz, we have enhanced the LinearPhase PEQ Orange with low-noise and low-distortion oversampling technique. There are two different oversampling filters optimally calculated for 44.1 kHz and 48 kHz. They are automatically selected according to the sampling frequency of the input signal. The THD+N of these filters is below the noise floor of a perfectly recorded 24-bit audio material. This means that the oversampling process absolutely does not degrade even perfect 24-bit quality signals. Therefore we highly recommend always keeping the oversampling filter on.
• In general, the LinearPhase PEQ Orange sounds more analytical than its brother, the LinearPhase PEQ Red, and therefore is specially recommended for difficult mastering and re-mastering tasks on dense mixes. For subjective opinions about experiences with both the Orange and the Red click on the respective menu point “Client Testimonials” and read what our customers say.