SPL Audio Mic-Pre/EQ

The EQ MAGIX is a single-channel equalizer system consisting of a para metric and a psychoacoustic equalizer. Both are combined with a superior microphone preamplifier and an active two-channel panorama output stage.

The EQ MAGIX is ideally suited for both a demanding instrumentalist or a singer's rack. Existing equipment can be looped into the signal path

INSERT. The unit's outputs are either connected directly with the recording medium or with one to four (2x balanced and 2x unbalanced) mixing channels. From there, the signal is fed into the Insert Return after the section (provided that appropriate Insert points are available), so as bypass as much desk circuitry as possible. As you know, a signal is influenced if all the switches are on »off« and all controls are in the centre position or on »0«. That is why it is advisable to feed the signal in after desk equalizer.

The technology in the microphone preamplifier is used in the very latest generation of mixing desks made by Harrison and SSL. The parametric equalizer of the EQ MAGIX is based on SVF design (state-variable-filter) and provides a operation frequency range between 14 Hz and 58 kHz. The integrated VITALIZER was developed by SPL and has achieved a significant degree of popularity over the years. The filter concept works on the basis of psychoacoustic sound principles and is therefore ideal to achieve creative sound effects. The combination of a flexible parametric EQ and VITALIZER means that the EQ MAGIX is not only predestined to process the sounds of acoustic instruments but also to post-process samples or poor quality Sync audio tracks, ranging from the elimination of aliasing artefacts or other digital interferences to the addition of sub basses or comprehensive sound impro- vements via the VITALIZER.

The EQ MAGIX provides you with equalizer technology which is unri- valled in comparable units. You will find that this equalizer can not only be set quickly and accurately at the desired frequencies but, with the aid of loudness sound control, can also form sound patterns which cannot be achieved with conventional equalizers.

The section below contains a brief description of the EQ MAGIX's func- tion groups:

1. INPUT: Microphone and line level signals can be preamplified in the INPUT section. Microphone signals can be preamplified up to 65 dB. Activating the LINE switch attenuates the preamplifiers stage by -30 dB. There is a phantom power supply (48 V) for condensor microphones. The PHASE REVERSE switch is used to change the polarity of the microphone. The PEAK LED provides adequate warning of potential overdriving of the output stages in the INPUT section.

2. INSERT: Additional sound processing equipment such as a compressor, de-esser or reverb can be looped into the EQ MAGIX via the INSERT jacks. The INPUT section can be used separately for one signal, whilst the equa- lizer sections are available for a second signal. Use the INSERT SEND as the output for the INPUT section and the INSERT RETURN as the input for the second signal.

3. PARAMETRIC: The PARAMETRIC equalizer is to boost or cut different frequencies or to cut out specific interference noise signals. It is, in a manner of speaking, a corrective instrument in the EQ MAGIX chain of sound-processing tools. The PARAMETRIC works according to the constant-Q principle. The frequency ranges between 14 Hz and 58 kHz. The control characteristics of the bandwidth (Q) control ranges from Q0.6 to Q3.6 and can be sensitized via the Q-FINE switch to set more subtle Q values. The boost or cut range is max. +/-15dB. The integrated NOTCH filter can be controlled in frequency, bandwidth and also in the filter slope (ROLL-OFF) from gentle decreasing or increasing (GENTLE) to steeply decreasing or increasing (STEEP). This significantly increases the tonal flexibility of the NOTCH Filter.

4. VITALIZER®®: The VITALIZER is an equalizer concept which makes use of scientific psychoacoustic technology to process audio signals. The unique combination of dynamic equalizers, amplitude-controlled phase correction and harmonic filtering in the VITALIZER opens up a whole new listening dimension by adapting the sound pattern to the non-linearities of the human ear. The VITALIZER is thus the creative element amongst the EQ MAGIX's sound processing tools.

The VITALIZER gives the mid frequencies accurate transparency with a soft, unobtrusive sound. The treble and harmonics range is reworked with broadband shelving filters of 2nd and 4th order, which focus on achieving a smooth, silky sound pattern. High frequencies are livened up without them sounding hard or agressive.

The VITALIZER uses a newly developed filter network to process the low frequency range. The bass is accentuated without any risk of emphasizing the lower mid frequencies unnaturally. You can choose between a dry, percussive bass (TIGHT) or a punchy, soft and very deep sound character (SOFT). The result is a pleasanter and livelier sound pattern with an unrivalled wealth of detail. You will be amazed by how transparent and powerful almost every audio signal sounds after it has been processed with the VITALIZER!

1. OUTPUT: The OUTPUT section enables you to create a two-channel output signal from a one-channel input signal. You can return the signal to two desk channels or feed it directly into a multi-track recording medium or effect unit. Balanced outputs available via XLR sockets and unbalanced outputs available via jacks can be used in parallel. A signal can therefore be recorded on two media simultaneously. On the front panel, two bargraph meters each featuring 10 LEDs provide information about the output level of each channel. The indication of PPM values (peak values) provide more information than a VU display (average values). The MUTE switch can be used to mute the output signal altogether. The PANORAMA control allows active panning between the two output channels, compensating the loss in volume (- 3dB) which arises in conjunction with panning to one channel. The FADER switch alters the characteristics of the PANORAMA control, making it an output level control. The output level can be reduced for both channels to compensate diffe- rences in the levels of the processed and the dry signal.

The EQ MAGIX features a PARAMETRIC constant-Q equaliser combined with the VITALIZER equaliser system. This combination of filters is based on the assumption that after succes- sful microphoning, you only have one problem zone, if at all, that needs to be equalized. The VITALIZER provides all the necessary circuitry for creative sound post-processing.

The EQ MAGIX provides a total of five processing ranges: the PARAME- TRIC section provides an extremely variable and efficient filter for selective intervention in a frequency band between 14Hz and 58kHz. The VITA- LIZER interferes in 4 frequency ranges, bass, mid and treble, along with the harmonical frequencies pertaining to even and odd overtones.

The PARAMETRIC section is designed to clean up one »problem zone« in the frequency spectrum of the recorded instrument or voice perfectly, without prejudicing the sound and without being inhibited by technical limitations of standardized filter circuits.

The equalizer used in the EQ MAGIX is based on the state-variable filter type (SVF). Its function is phase-stable and neutral right down to 14 Hz in the infra-sonic range. The frequency range extends right up to breath- taking 58 kHz! This initially provides a platform for experimentation as to whether interspersing digital components affects into the tonal perception range (16 Hz to 20 kHz) or whether the removal thereof can remedy sound problems directly or indirectly. We have visited sound engineers and producers in European and American audio and video studios and they pointed out to us that inter- spersing the sample rate frequencies (44.1 kHz and 48 kHz) into the audio path is a well-known phenomenon, whereby subharmonic elements can be transposed right down into the audible frequency spectrum. Furthermore, this can result in audible phase shifts and distortions. With the EQ MAGIX, you can now influence these frequencies actively. The sample rate frequencies are inscribed on the scale (44, 48).

All frequencies can be boosted or cut with 15dB throughout the entire frequency range from 14 Hz to 58 kHz. The PARAMETRIC equalizer of the EQ MAGIX is based on the constant-Q principle and provides an »inversible Q«, i.e. when filtering out a interfering frequency, inverting the boost value to a cut value results in precise inversion of the bandwidth (Q) values. Notching is also possible with a variable ROLL-OFF to select a STEEP or GENTLE filter slope. Extremely flexible bandwidth defintion allows Q values between 0.6 and 3.6.

The VITALIZER is the creative sound component in the EQ MAGIX. It works »intelligently«, provided the appropriate parameters are preselected. This means that it does not just raise or lower a certain frequency range but analyses the signal and reacts to it, influencing the frequency and phase response in a sophisticated fashion.

Independently of the potentiometer settings on the front panel, the VITALIZER filter system can correlate the phase and amplitude relations of adjacent frequency bands in such a way that the increasing amplitude of a frequency is given a growing phase drift which, however, can never endanger the signal's mono compatibility. The maximum phase drift is +/- 20° which equals a time difference of around 1 ms to 2.5 ms. This time span is sufficient to trigger two hearing perceptions. Quiet frequencies which are normally masked by louder ones are effectively demasked and thus become audible. The front panel also accommodates controls to define the bass sound colour (SOFT/TIGHT), the starting frequency of the MID-HI TUNE filter, the PROCESS intensity and the addition of the harmonics.

The BASS control provides up to 20 dB gain, thus affecting the direction of the phase drift by the bass sound colour selected. The fact that the phase drift is controlled by the amplitude means that even high bass amplifica- tion remains free from negative sound colouration in the lower mid range. The mid-high frequency filter (MID-HI TUNE) works with shelving filters which provide »linear« broadband amplification. This rules out any comb filter effects which create sound distortions similar to those produced by graphic equalizers.

The PROCESS control determines the addition of the bass sound selected and the MID-HI TUNE filter to the dry signal. In addition, dominant mid frequencies are lowered by phase shifts which means that as the PROCESS value increases, they are adapted automatically to curves of equal loudness (Fletcher-Munson curves). The PROCESS is, in a manner of spea- king, an »intelligent« loudness control which can be used to set the typical »bath-tub« curves on graphic EQ's by turning one potentiometer. The HARMONICS circuitry provides a silky sounding, refreshed version of the original signal. This proves particularly beneficial for voices and acoustic instruments. No distortions are added to the original as there is no Exciter involved. The filters merely amplify the harmonic tones contained in the original.

The EQ MAGIX is constructed like a mixing desk channel. Direct recor- dings can be made on to a recording medium (multi-track machine or hard disk) which means that one less mixer channel is required.