SPL Tube Vitalizer

Stereo program equalizer

SPL Tube Vitalizer Stereo program equalizer

Review by George Shilling

The Tube Vitalizer looks impressive, with a nod towards vintage valve equipment. It is a 2U steel box, with a bare metal front panel. There are plenty of black knobs, and three grilles revealing glowing tubes. Actually, most of the glow comes from the lamps illuminating the little VU meters.

Below these, two old-fashioned black knobs are labelled "ATTENUATOR". Switches light up red when pressed in, apart from a couple of metal toggles, and there are blue LEDs to show High and Low frequency compression. When you switch on, your attention is drawn to two LEDs, proudly labelled "TUBE STATUS", with the "WARM UP" one glowing for 45 seconds before a relay kicks into "ACTIVE" mode. During this 45 second period the circuitry slowly builds up to 250 volts to increase the life of the valves. This is sensible, but I am not sure that the LEDs are really necessary. The back panel features XLR connectors and also plastic balanced jack sockets for inputs and outputs. The unit runs at +6dB instead of the more usual +4dB. Jack connectors are also set to +6dB operation, unfortunately without a switch to enable -10dB operation.

The Process Level control works like the Loudness button on your hi-fi. Above a frequency set with the High-Mid Frequency control (22kHz down to 1kHz) it applies a shelving EQ boost. Simultaneously there is a low frequency boost centred at approximately 50Hz, and a mid cut centred at about 1.5kHz. The manual states that the Process achieves mid damping by "amplitude-controlled phase shifting", and claims that this improves the perception of loudness, clarity and bass punch. It sounded little different from conventional EQ in practice.

SPL Tube Vitalizer Stereo program equalizer

There is some explanation of Fletcher-Munson curves in the manual, which then makes the astonishing claim that "The Tube Vitalizer alters the frequency spectrum in such a way that the balance is maintained between all frequency ranges even at varying monitor volumes". This is hard to swallow, as most of you will know that Fletcher-Munson curves show the ear perceiving less HF and LF as volume decreases. There is a drive knob to control the intensity of the processing which adds a warmth and subtle distortion when increased. The Bass control is labelled Soft to the left and Tight to the right. Turning the knob in either direction should intensify the bass sound, but this is not what I perceived. Tight seemed to boost the low end, but Soft seemed to decrease bass content of the signal. Bass Comp. compresses only the low frequency content of the signal. There is an LC Filter which adds a passive coil/condenser filter to the resistor/condenser filter network. There is some enrichment of the sound with this added, midrange as well as low frequencies seemingly affected..

 Unlike some "exciters" the Tube Vitalizer's High EQ and harmonic filters do not add distortions to the original signal. So what do they do? Well, they do not say exactly, but it SPL claim that the processor extracts all the information needed from the original signal. "By influencing the phase relationship in an intelligent fashion, the filtering emphasises the perception of high and harmonical frequencies." The Intensity knob adds HF gain, and the HF control apparently sets the shelving frequency. The manual claims that this section picks out particular frequencies, but the accompanying graph (tracing response with Intensity and Frequency both set at 10) shows a plain 4dB shelf boost from about 4kHz upwards, or 2kHz when the adjacent LC filter switch is pressed. The third knob in this section is labelled High Comp. which compresses only the high frequencies. It is possible to brighten the signal and then compensate with this knob, giving little audible change except for some subtle compression. By pressing the Activate Tubes switch the output stage is swapped over from solid state circuitry. In this mode can you use the Attenuator knobs to compensate for any gain during processing. The valves add a pleasant warmth and depth to the signal. Each channel has a toggle switch labelled Atten./Limit.

The manual states that in Limit mode all signals above the 0dB mark will be softly limited. Audibly, signals below this point are affected by distortion, and the sound is not dissimilar to a guitar overdrive pedal. Despite the switch labelling, the Attenuate knobs still attenuate. With a piece of equipment such as this you need to hear it yourself to evaluate whether you like it. I could imagine using it on particular instruments in a mix, or when recording, to bring them forward. It usefully adds a bit of sparkle to a part in need of something special, but I am not sure I would want to use it across an entire mix: amazingly the manual itself admits that the brain soon acclimatises to changes of timbre, which surely defeats the object.

The manual is full of pseudo-scientific claims and techno-babble, and there are a few typographical errors, but as the unit is of German origin, perhaps it loses something in the translation. Not essential, but for something a bit different, on occasion this might be your box.

Reproduced with kind permission from Copyright ©

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