Stereo Mastering Highpass Lowpass Filter with Phase Correction
The W790 combines a set of filters for limiting the band width with stereo mastering. Adapted frequency ranges to mastering applications that reach far beyond the audio band, steepness selection, and the possibility to control both stereo channels with independent controls are implemented. High-pass und low-pass filters have a steepness of 12 dB/oct. that can be switched to 6 dB/oct. The additional phase correction circuits allow adjustable compensation of the phase shift that is caused by the high-pass and low-pass filters. The phase shift circuits can be switched to compensate 6 or 12 dB/oct. steepness settings. Separate adjustment of the stereo channels is also possible. Since the phase correction circuits are entirely independent, they can also be used to compensate the phase response of a mix without using the high-pass and/or low-pass filters.
The W790 is the result of suggestions and ideas of many customers to design a high-pass low-pass filter especially for the particular needs of mastering. Usual filters don't have appropriate control ranges for this criticle adjustments and usually do not allow bypassing the high-pass when only the low-pass is used and vice versa. The separate adjusment of both channels is also a very useful features for special treatments.
Since each filter that alters the frequency response also alters the phase response, and this results in additional tonal changings, we have added an adjustable phase correction circuitry to the filters, which can compensate the phase error caused by using the filters. Furthermore, the phase correction can be used indepently to correct the phase response of a mix as well as fine tune the phase accuaracy of the stereo channels that effects the stereo base width and the accuracy of the location of signals on the stereo base a lot. In total the phase correction circuits adds many possible, subtle treatments and allows compensation of prior problems that can improve the mix considerably.
High-pass and low-pass filters have a slope steepness of 12 dB/oct. The 'maximum flat' filters can be switched to 6 dB steepness with independent switches for high-pass and low-pass. The SPLIT switches allow idependent regulation of the two stereo channels. The upper control is used in stereo mode and for the left channel; the lower control is used for the right channel and it is only active when SPLIT is pressed.
The sweep range of the low-pass filter reaches from 8 kHz up to 100 kHz. Such high frequencies will alter neither the phase response nor the frequency response at 20 kHz. Starting with 100 kHz makes possible to precisely reduce the upper limit frequency to the point where either the phase response or the frequency response of the filter curve results in audible changes.
The sweep range of the high-pass filter reaches from 100 Hz down to 5 Hz, which offers using the same adjustment procedure for the low frequency range. Both filters have separate bypass switches.
The Phase Correction Filters are controlled by additional pots that use the same scaling as the high-pass and low-pass filter controls. Corresponding settings result in a compensation of the phase shift. If set differently, the phase shift of the high-pass or low-pass filters is either under or overcompensated. The 6 dB switches adapt the phase correction circuitry to the slope steepness of the high-pass low-pass filters. The SLPIT switches select independent regulation of the two channels. The upper control of each section is used for the left channel and the lower control treats the right channel when SPLIT is pressed.
The phase correction circuits can be used inpedendent of the filters. Correction of the phase response of prior filtering is possible as well the general correction of the phase response at the upper and lower end of the audio band and the phase accuracy of the stereo channels. Considerable phase shift in the low frequency range results in unprecise, spongy bass performance, while high frequency phase shift causes softer or harder highs. Any phase difference between the stereo channels is very criticle, since it narrows the stereo base and blurs precise location. These phase errors are audible even if the phase shift is only some degrees.
Due to the versatile possibilities for controlling the phase response, many of these problems can be covered using the phase correctrion circuitry.
The module is available with electronically balanced or transformer balanced inputs and outputs. The maximum level is + 30 dBu.
A hard bypass connects inputs and outputs of the unit and floated the internal inputs to avoid load on the source signals as long as the ON switch is released. In addition the the main bypass, there are single bypass switches for each filter section.
The stereo mastering high-pass low-pass filter with phase correction W790 is a single slot V700 module that fits into all V700 standard frames.