Stretched Tuning: Why “In Tune” Isn’t Always Correct
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Stretched Tuning: Why “In Tune” Isn’t Always Correct
Spend enough time around acoustic instruments and you start to realise something slightly counterintuitive: perfectly “in tune” isn’t always what sounds right. In fact, in many cases—particularly with pianos and piano-derived instruments—strict mathematical tuning can sound subtly off, even when every note lines up exactly with a tuner.
That’s where stretched tuning comes in. It’s one of those details that sits just below the surface of most recordings: rarely talked about, but immediately noticeable when it’s missing. At Resonance Studios in Stockport, Manchester, it’s something we pay close attention to—especially when working with instruments like the Yamaha CP80, where the relationship between physics and perception is impossible to ignore.
The Problem with “Perfect” Tuning
Most modern tuning systems are based on equal temperament—a compromise system that divides an octave into twelve equal parts. It’s practical, flexible, and works across all keys, which is why it became the standard.
But equal temperament is just that: a compromise.
In theory, each note sits exactly where it should according to a mathematical ratio. In practice, though, our ears don’t perceive pitch in such rigid terms. More importantly, real instruments don’t behave like perfect mathematical models. Strings have stiffness, mass, and physical limitations that introduce slight deviations from ideal harmonic behaviour.
On a piano, this becomes particularly obvious. Each note doesn’t consist of a single pure frequency—it’s made up of a fundamental tone and a series of overtones (harmonics). Ideally, those harmonics would line up perfectly in neat integer multiples. In reality, they don’t. This phenomenon is known as inharmonicity.
And it’s the root of the problem.
What Is Stretched Tuning?
Stretched tuning is the process of deliberately adjusting notes across the range of an instrument so that they deviate slightly from equal temperament. Typically, this means tuning the higher notes a bit sharp and the lower notes a bit flat relative to their theoretical positions.
It’s not random—it’s carefully judged.
The goal isn’t to “fix” the instrument, but to align what we hear with how the instrument actually behaves. By stretching the tuning, we compensate for inharmonicity and bring the overtones into a more perceptually pleasing relationship.
Without this adjustment, intervals—particularly octaves—can sound narrow or slightly dissonant, even if a tuner says they’re correct.
With stretched tuning, those same intervals feel open, balanced, and natural.
The Origins of Stretched Tuning
Stretched tuning didn’t emerge from theory—it emerged from practice.
Long before digital tuners existed, piano tuners relied entirely on their ears. They would tune intervals—particularly octaves—by listening for “beats” (the interference patterns between slightly mismatched frequencies). The aim was to minimise or control those beats in a way that sounded musically coherent.
Over time, tuners noticed something consistent: if they tuned strictly to theoretical pitch, the instrument didn’t sound right. The higher registers felt cramped, and the lower registers lacked depth.
The solution was to stretch the tuning.
This wasn’t written down as a formula at first—it was passed down through experience. Skilled tuners developed an intuitive sense of how much to stretch different parts of the keyboard, based on the specific instrument in front of them.
Even today, despite the availability of highly accurate digital tuning systems, that human judgement still plays a crucial role. Modern tools can assist, but they don’t replace the ear.
Why Pianos Need It More Than Most Instruments
All stringed instruments exhibit some degree of inharmonicity, but pianos are particularly affected due to their construction.
Piano strings are relatively thick and under high tension. Their stiffness causes the overtones to deviate more significantly from ideal harmonic ratios. The shorter, thicker strings in the upper register are especially prone to this effect.
As a result, the higher notes naturally “want” to sit slightly sharp compared to their theoretical positions, while the lower notes tend to feel more comfortable slightly flat.
If you ignore this and tune everything strictly, the instrument fights back. Octaves don’t line up perceptually, chords feel uneven, and the overall sound loses coherence.
Stretched tuning works with the instrument’s physical properties rather than against them.
The Yamaha CP80: A Unique Case
The Yamaha CP80 sits in an interesting space between acoustic and electric instruments. It uses real strings and hammers, like a traditional piano, but instead of relying on a soundboard, it captures the vibration through pickups.
That hybrid design brings its own set of characteristics—and its own challenges.
On one hand, the CP80 retains the physical behaviour of a stringed instrument, including inharmonicity. On the other, its amplified nature makes tuning inconsistencies more exposed. There’s less acoustic blending, less natural masking.
In other words, if something is slightly off, you hear it.
This makes stretched tuning particularly important. Without it, the CP80 can sound brittle in the top end and unfocused in the low end. With it, the instrument opens up—becoming more balanced, more musical, and far more usable in a mix.
Why It Matters in a Recording Context
In a live setting, small tuning discrepancies can often go unnoticed. The environment, the acoustics, and the energy of the performance all play a role in smoothing things over.
In the studio, everything is exposed.
Microphones (or in the case of the CP80, direct pickups) capture detail with a level of precision that leaves very little room for error. Once recorded, those details are effectively locked in.
If an instrument isn’t tuned correctly—perceptually correctly, not just mathematically—it can create subtle issues that are difficult to fix later. Chords may feel slightly off. Layered parts might clash in ways that are hard to identify but easy to feel.
This is particularly important when working with other harmonic instruments, such as guitars or synthesizers. If the piano isn’t sitting correctly, it can throw off the entire harmonic foundation of a track.
Stretched Tuning at Resonance Studios
At Resonance Studios in Stockport, Manchester, stretched tuning isn’t treated as an optional extra—it’s part of the preparation process, especially when the Yamaha CP80 is involved.
Before recording, the instrument is assessed not just with a tuner, but by ear. Octaves are checked across the range, listening for how they sit rather than where they sit. Adjustments are made gradually, taking into account the specific behaviour of that particular instrument.
No two pianos—or CP80s—are exactly the same. Age, string condition, environmental factors, and previous maintenance all influence how an instrument responds. That’s why a one-size-fits-all approach doesn’t work.
The aim is always the same: to create a tuning that feels natural across the entire range. One where chords sound balanced, intervals feel open, and the instrument sits comfortably alongside everything else in the session.
The Subtlety (and Importance) of Getting It Right
One of the interesting things about stretched tuning is that, when it’s done well, you don’t notice it. The instrument just sounds “right”. It’s only when it’s absent—or poorly executed—that the problems become apparent.
This subtlety can make it easy to overlook, particularly in an era where so much emphasis is placed on visible or measurable aspects of production. But in practice, it’s one of those foundational details that can elevate a recording from good to great.
It’s also a reminder that music isn’t purely mathematical. Our perception of sound is shaped by complex interactions between physics, biology, and experience. What matters isn’t just accuracy, but how that accuracy is interpreted by the ear.
A Small Adjustment with a Big Impact
In the grand scheme of a recording session, stretched tuning might seem like a minor detail. It doesn’t have the immediate impact of a microphone choice or a performance decision.
But it underpins everything.
When an instrument is tuned in a way that aligns with both its physical properties and our perception, it becomes easier to work with. Parts sit more naturally. Mix decisions become simpler. The overall result feels more cohesive.
At Resonance Studios in Manchester, serving artists across Stockport and beyond, that kind of attention to detail is part of the approach. Whether it’s a vintage synth, a tape machine, or a Yamaha CP80, the goal is the same: to capture sound in a way that feels right from the outset.
Because in the end, that’s what good recording is about—not just precision, but perception.