This is evident by the regular need of technicians to take steps beyond the built-in automatic capabilities of their ETD in order to obtain the best results, by either:

• making aural adjustments where the machine's tuning does not sound the best,
• creating multiple tunings to better fit the different sections of the piano, or
  
• resorting to a complicated series of manual steps that uses the machine to perform comparisons of one tuned note to another as in aural tuning.

The need for these techniques is usually just accepted as a limitation of the state of the art and is fully acknowledged and taught by the ETD manufacturers. The advice usually given is "your ear is the final guide, don't forget to listen". This is great advice; the ear should never be taken out of the equation. But why not strive for an ETD that requires the least amount of tuning rework? The methods of either aurally adjusting an ETD tuning or using manual ETD tuning steps require extensive aural tuning knowledge, and will result in variations in the quality of results depending on the skill level (or fatigue level) of the technician.

The shortcomings of ETD tunings are actually related to their failure to hear all the partials that an aural tuner does. Most ETDs tune with a sort of tunnel vision by tuning to only one partial on most notes of the piano. This is limiting, because in reality every note consists of a multitude of partials. Each of these partials is heard by the ear. More importantly, each of these partials separately contributes to important tuning intervals.

If the inharmonicity across a piano's scale were consistent and could be accurately predicated, tuning to one partial of each note would be sufficient, because the pitches of the untuned partials could be accurately predicted. But for the majority of pianos, the inharmonicity is not consistent. If the ETD has no knowledge of the inharmonicity of each note, then it has no knowledge of the pitches of any partial besides the one being tuned. The pitches of these other partials are heard by the ear and contribute significantly to the quality of the tuning.

Of course multi-partial tuning is not new. Aural tuners have always tuned this way through the use of test intervals or "checks", and through the multiple beat rates heard at different partial levels when tuning octaves. A multi-partial ETD has a major advantage in tuning quality over one that does not. How much of a difference does it make? Take a look at our case studies, and you will see multiple partials in action.