Phoenix Gold Titanium TiDEQ Digital Car Equalizer

A technical marvel, the Phoenix Gold TiDEQ is a stereo, digital, 30-band EQ and time delay unit with analog inputs & outputs.

Cosmetics
The Phoenix Gold TiDEQ equalizer simply looks fantastic. With its three blue LEDs, four translucent Plexi covers, and brushed aluminum chassis, this has to be one of the best looking equalizers out today. The internal layout is nice too -- housing power supplies, AD/DA converters, and two Motorola 24-bit digital signal processors (DSPs). Audio inputs and outputs are standard-issue gold-plated RCA connectors.

Mechanical Controls
Total Setting control for the TiDEQ can only be performed with the use of a PC, using the Windows-based software provided. There are no level or gain adjustments on the unit itself. Four presets can be made (SPL, RTA, SQ, and User) and controlled through a remote panel with blue LEDs that can be mounted within reach of the driver. The other option for changing the settings is the TiDEQ Comp Remote Control Unit (MSRP $299.00). This unit is available and plugs directly into the TiDEQ and can be mounted anywhere in the vehicle. This gives the same setting control as the use of the PC and the windows based software with the exception that the "Q" cannot be adjusted per the band of equaliztion.

DSP Background
Processing a signal digitally can happen in two ways: One is to take the signal, usually 16-bit, 44.1 kHz, directly from the digital source, process it, convert it to analog and present it to the output connectors. The problem with this approach is that the volume must now be controlled after the digital processing to preserve fidelity. This would preclude any controls in the audio chain ahead of the DSP, preventing even simple volume and fader adjustments.

The second approach, used in the TiDEQ, is to accept an analog signal, convert it to digital, process it and convert it back to analog. In this scenario the audio signal is converted three times, once to make the CD, and twice within the TiDEQ. The problem with this approach is that the input signal is not usually at the correct level to take advantage of the full digital resolution available in the DSP. However, the TiDEQ uses excellent Crystal 24 AD/DA converters. This allows the audio signal to be resolved to one part in 16 million, which reduces scaling problems found in older DSP technology.

Performance
Software installation--A Windows program is used to configure the TiDEQ. Installation went smoothly without any hickups. However, the serial port parameters must be set every time the software is installed. This quirk becomes tiresome if the program is running from an on-board computer. The user has to set the serial port every time the program starts up. On the flip side, this allows the program to be used with multiple TiDEQ's without effecting the current settings - a sort of safety feature.

The unit worked flawlessly, satisfying virtually every conceivable requirement for equalization, crossovers, and digital delay. Signal-to-noise was a respectable 102 dB, "A" weighted. Harmonic distortion was typically under .01 % THD+N, rising to .03% at 6 kHz. We also did a distortion sweep at 500 mV. This causes the 24-bit converters to operate using just 21 bits. THD+N at this setting was still a very respectable .02% across the entire frequency spectrum.

Because each of the 30 filters has an individually selectable Q, virtually any type of equalization can be accomplished. Add three fully parametric filters, digital delay, and variable 12/24 dB/Octave crossovers to satisfy your other needs!

The TiDEQ can be configured as a single-channel crossover, but not stereo. In this configuration, we tried our crossover summation test. This simulates the two-way acoustical summation of an ideal speaker system. The 12-dB/Octave crossovers had a typical dip at the crossover point, typical of an analog crossover. But this could be corrected to 1.5 dB by inserting the right amount of delay. The 24 dB/Octave crossovers summed to an excellent 0.5 dB without using delay. This is a nice advantage over analog crossovers.

Each of the 30 filters plus the three parametric filters is capable of +6, -18 dB boost/cut. This non-symmetrical parameter helps avoid clipping problems and allows the input level to remain high. Using a lot of boost would force very low input levels, which would reduce the digital resolution.

General
Crossovers--To use the system as a digital, two-way crossover, you need two of them. Phoenix Gold doesn't claim to incorporate crossovers, just adjustable high-pass or low-pass filters. While the 24 dB/Octave slope of the high pass filter can be used for a subsonic filter, a steeper slope would be desirable. This unfortunately is a standard slope amongst most subsonics filters.

Input level adjustment--There is no adjustment of input level. If the input is set too high, the unit clips. While 4 volts is the maximum level, signal levels at 3 volts could cause clipping if too much boost is used in the equalizer settings.

Output Attenuators--When we forced the unit to clip with the output attenuated, the clipping LEDs failed to come on. We recommend leaving the output attenuators at 0 dB to prevent this situation.

Source impedance--Our measured noise levels increased by 5 dB, going from a source impedance of 20 ohms to 600. Using a low output impedance deck is desirable.

GUI--The graphical user interface works well. The only concern is the 600 x 800 pixel resolution may not be usable with some on-board displays.

Q--This is an excellent idea and makes for a very versatile equalizing process. Unfortunately, Phoenix made a mistake with their Q definitions. Their reported Q of 7 should really be 4.2. That means that all of the other Q measurements are off. This doesn't affect anything sonically, but they need to revise their software and owner's manual.

DSP Scaling--Normally the volume control is ahead of the TiDEQ. With normal listening levels, the input may be in the range of 15mV. This forces the equalizer to work with much less resolution, such as 15-16 bits. For the purist, I'd recommend controlling the volume after the TiDEQ to improve SNR and distortion, while keeping the digital signal near maximum.

Size--The unit measures in at 14" L x 10.25" W x 2.25" H. A little large, but it does house 68 filters, plus time delay!

Listening Test
Our listening test revealed little problems. Sound quality was good otherwise; no anomalies were detected.

A very slight audible hiss was heard with the amplifier set to 1-volt sensitivity even though our SNR measurements were above 102 dB.

The majority of the noise issues were detected while making adjustments. With the computer connected to the RS-232 interface, we also heard motor noise from the CD player. Disconnecting the computer eliminated this source of noise. Also, isolating the computer from the 12 volt ground solved this noise problem as well. Not to worry. Another noise problem was also noticed with the computer connected. Changing the filter settings via the Windows program caused a quiet chirping noise, but disappeared with ground isolation.

Conclusion
The TiDEQ is a technical marvel. The amount of processing required for this many filters is huge, necessitating the use of two 24-bit DSPs. Digital delay is sorely needed in many installations and cannot be duplicated in the analog realm. The four presets will come in handy to quickly switch between complete sets of filtering and time delay. This equalizer should resolve any filtering requirement.