Tone Controls

For purists, the thought of deviating from short, unprocessed signal paths is taboo. For the last 20 years tone control-free preamps have been made for them. The reason is obvious: tone controls introduce "grain," colorations, deterioration, or coarse boosts/gains at the wrong frequency, with the wrong slope for the specific adjustment needed (this always seemed to me the key problem with the tone controls on Accuphase amps). This has not stopped a few high-end manufacturers from including high-quality tone controls on their preamps and integrateds (e.g. the Cello Audio Suite) which gives you precise tonal shaping of playback with "very little" loss to the signal. Even so, I've yet to hear an analog tone control bank with "negligeable" loss to the signal. The solution seems to be--as "Keis" put it--to push tonal shaping into the digital domain (negligeable losses, no added coloration) and give the user more precise control over the shaping. This has already been done on the z-systems digital preamp with their Transparent Tone Control (TTC) system. TTC is so precise and uncolored that it will probably change the prejudices purists have about tone controls. Of course, you can use TTC as a tone correction system on a recording-by-recording basis and dial in specific EQs for each recording (then store the setting on one of the 100 presets), but what makes this system exciting is the possibility of achieving a tonally balanced system and listening space. If you use a state-of-the-art calibrated mike and spectrum analyzer, you can refine the sound of your system to virtually flat response. Even the most expensive speakers in the world (the Wilsons, the Avalons, the LumenWhites, etc.) require boosts/gains at certain frequencies in order to yield a flat frequency response. The end results are well worth the hassle of using this system: you will have a tonally balanced system, with greater low-level detail, more immediacy, more extended bass or highs, more openness, an impression of greater speed, an improved spatial presentation, and experience less fatigue. On the forum "Applying EQ to STAX" (Tech. Talk) I describe the use of the z-systems TTC to flatten out the frequency response of the STAX earspeaker system. I have done the same with all of my loudspeakers as well (to achieve neutrality over all hearable frequencies even expensive floor standers need as much as 5 dBs boost at 31Hz, monitors as much as 10dBs boost at 56Hz). Even if this involves the rental or borrowing of a calibrated mike and spectrum analyzer, or complex mathematical calculations to arrive at the proper slope or Q of each boost. This solution seems to me better than coarse analog tone controls or trying to use cables and room treatments as tone correction systems. To conclude, TTC is just another type of purism: not the no-tone-controls purism of the 1990s, but the DSP-tweeked-neutrality purism of the 21st century.

A few comments about analog and digital EQ.

There are any number of outstanding sounding analog EQ units (Avalon, GML. Manley, Millennia, etc.) on the market. Although clearly aimed at the pro audio market, they are easily incorporated into a component based high end system. The Manley unit is of particular interest in that its a tube design.

Digital EQ offers enormous potential for audiophiles. It can be both precise and unobtrusive even at extreme settings. I use a 5 band parametric unit by Drawmer. The bottom three bands are used to correct for the room's bass response and the two other bands are used as tone controls to shape the treble. As with analog circuitry, there are large sonic differences between digital EQs products.

If you use either analog or digital EQ, don't equalize your system for flat response at the listner position. It will sound way too bright. Aim for a smooth response with a downward sloping response from the upper mid-range on up. Also, don't try to EQ out the narrow band, sharp response dips in the bass region that are inherent in nearly all rooms. Even the Sigtech or TACT processers don't try to remove these sonic "sink holes". Trying to get rid of them will create boomy bass at every other listner position in the room as well as robbing you system of dynamic headroom.

Onhwy61, your comments are well-considered and very helpful. Would like to know what sonic differences you have discovered between digital EQ products. --What is striking with the z-systems TTC is the large sonic variations achievable through line filtering and power cord substitutions--just as with most digital equipment. --Once I achieved a flat response at the listener position, I noticed the brightness you mentioned and developed a second EQ setting with slow downward sloping response from 8-9kHz onwards. The STAX earspeakers required this downwward hi-freq. slope from the very start, because of their etch (a cause of much fatigue and even pain, and even the desire to sell them). --To perfectly EQ the narrow-band irregularities in the bass response of a room loudspeaker would require too many bands of EQ, so that none would be left for other purposes, and yes the dynamic headroom significantly decreases. --Some consideration always needs to be given to maximum smoothing effect with the number EQs one has at hand (of course, one can always run two units in series...). --Given your description of your EQ settings, it seems that you do not EQ any mid-range: lucky you, as every speaker in my possession has irregularities in both low and upper mid-range freq. response (e.g. 1.4kHz-3.0kHz; and 5.0kHz-7.0kHz). Perhaps the happiest result of digital EQ on two-way monitors was to hear significant low frequency from them, and a linear mid-range corrected for obtrusive crossover irregularities.

Slawney, I purposely left the mid-range untouched and used it as a reference for setting both bass and treble levels. I'm still learning how the use effectively use EQ, but I've noticed that even with EQ, standard audiophile practices still have to be observed. The EQ works best when the speakers are well positioned in the room. I could not compensate for poor placement with EQ. I tried and I was able to get better measurements, but it never sounded right.

As a room bass equalizer, the Drawmer works fairly well, but my system is such that I do not use it on SACDs or analog sources. As with most things in life, there are trade-offs.