THE PHYSICS OF QUIET / 02

Tracking Error in Audio Systems

Music is not only passed from one component to the next. It has to be tracked accurately while the conditions around it are changing.

An audio system is asked to preserve a musical event: its harmonic character, level and timing. In an ideal system, the signal arriving at the loudspeakers would remain faithful to the source. In a real system, the electrical and mechanical environment is moving too. High-frequency disturbance, vibration, grounding behaviour and power-supply interaction can all make that task harder.

This page uses a visual model to show the consequence. The green point is the musical reference: the route the system is trying to preserve. The blue point is the system response: close to the reference, but occasionally late, wide of the path, or high and low of the required level. That difference is tracking error.

The illustration explains the relationship between changing operating conditions and signal tracking. It is a conceptual model rather than measured product data.

A hare standing on a music stand in a recital room, illustrating the musical-reference metaphor.

The signal and the system response

The hare knows the route. The dog has to follow it across a moving field.

The visualisation is a way of seeing an idea that is normally difficult to describe. Think of the musical signal as a hare moving through a ploughed field. It changes direction, moves through the system and rises and falls in level. The system response is the dog trying to keep up. The dog has almost the same forward speed, but the ground is not still. As the furrows move beneath it, it can overshoot a turn, undershoot a change in level or arrive fractionally late.

That is the important distinction: the musical reference does not become less true because the environment is disturbed. The system’s ability to follow it becomes less exact.

  • Musical reference
  • System response
Illustrative signal-path plot. Frequency composition runs from left to right, amplitude rises vertically and distance recedes through the system. The moving field represents dynamic disturbance. A green musical-reference point follows the true path; a blue system-response point follows with tracking error set by Matrix insertion loss. Return loss changes the reflected field only. This is a conceptual illustration, not measured data.
The trace behind each point records where it has been. The wider the separation between green and blue, the greater the illustrative tracking error at that moment.
Frequency Composition The changing harmonic composition of the musical event. This is not a literal waveform or a spectrum-analyser trace.
Distance The signal’s route through the system, providing the sense of forward movement.
Amplitude The required musical level at that point in the route.
Green point and trail The musical reference: the path that remains true to the source.
Blue point and trail The system response: its attempt to follow the musical reference.
Moving mesh Dynamic disturbance: changing electrical and mechanical conditions around the signal. It is deliberately not an axis.

From tracking error to listening

Music asks the system to preserve relationships, not simply pass a steady test tone.

The most revealing musical moments are rarely simple or static. A vocalist changes inflection while a piano note decays. A drum transient arrives as an orchestra becomes denser. Small harmonic details need to remain distinct inside a much larger musical event.

Tracking error describes differences between the intended signal and the system response as the programme changes. Those differences can affect level, timing and harmonic structure without necessarily appearing as a separate buzz or hiss.

During our development and listening evaluations, reducing unwanted disturbance has repeatedly produced a clearer, more stable musical presentation.

These observations inform our investigation of signal tracking. Measurements identify how the response changes; listening evaluations examine its significance for image stability, transient definition, low-level detail and complex musical passages.

Quiet is not the absence of energy. It is the reduction of uncontrolled energy that can influence the signal.

Explore the Matrix boundary

Return loss controls what comes back; insertion loss controls what gets through.

Start with Without Matrix Absorption. The point source sits outside the area of interest, and unwanted high-frequency energy enters the system environment. The outer edge is deliberately a poor boundary, so substantial energy is reflected. The moving field remains energetic, and the blue response has more work to do.

Select With Matrix Absorption to introduce the Matrix boundary. The musical reference remains unchanged. Only the operating conditions and the system response change. The additional controls separate two related, but different, behaviours.

Higher return loss reduces the local noise at the Matrix entry.

At the entry boundary, unwanted energy meets the Matrix. Some of that incident energy could be reflected back toward its source. That returned wave adds to the local field and can reinforce the conditions that create standing-wave behaviour.

Increasing return loss means that a smaller proportion is reflected. The incoming disturbance has not been made smaller before it reaches the Matrix; rather, the Matrix sends less of it back. In the illustration, the total disturbance around the entry point falls because there is less reflected energy adding to the incident field.

Return loss is expressed as a ratio in decibels. In this conceptual model, the selected values correspond to the following reflected power fractions:

 

Matrix Return Loss Reflected power in this illustration
3 dB About 50%
6 dB About 25%
10 dB 10%
20 dB 1%
30 dB 0.1%

The Matrix Boundary

The Matrix sits between the entry and exit environments. It provides a controlled path for unwanted high-frequency energy, rather than allowing that energy simply to reflect or continue through the system.

At the entry: Return Loss controls how much unwanted energy is reflected back towards its source.

Through the Matrix: Insertion Loss controls how much unwanted energy is allowed to reach the downstream environment.

The musical reference remains unchanged. These controls affect the illustrative disturbance field around it.

Higher insertion loss reduces the noise that emerges from the Matrix.

Insertion loss describes what happens to the unwanted disturbance as it travels through the Matrix. Increasing insertion loss reduces the amount of that disturbance transmitted to the exit side. In the illustration, the field beyond the Matrix becomes quieter because less incident energy has been allowed through.

It is useful to see the two controls together:

  • Return loss reduces the reflected contribution at the Matrix entry.
  • Insertion loss reduces the transmitted contribution at the Matrix exit.

Together, reflection and transmission control reduce unwanted energy returning into the source-side environment and continuing downstream. Here, Return Loss and Insertion Loss describe unwanted high-frequency electrical energy. The engineering aim is to control that disturbance while preserving the wanted musical signal and normal power delivery.

Matrix Insertion Loss Transmitted power in this illustration
3 dB About 50%
6 dB About 25%
10 dB 10%
20 dB 1%
30 dB 0.1%

How to use the controls

  1. Begin with Without Matrix Absorption and follow the blue system response.
  2. Select With Matrix Absorption; the field becomes more controlled and the response moves closer to the green reference.
  3. Increase Matrix Return Loss to reduce reflected reinforcement at the Matrix entry.
  4. Increase Matrix Insertion Loss to reduce the unwanted energy that continues beyond the Matrix.
  5. Compare the separation between the two moving points, rather than looking for a single static shape.

From path to signal profile

Having seen the system’s path through an unstable environment, the next view shows the consequence in the music: how its frequency composition and amplitude change through time.

This second view uses the same Matrix settings, but looks at the changing musical profile rather than the route through the system.

Frequency composition, time and amplitude

A second conceptual view of the musical reference and the system response.

The reference trace changes in harmonic composition and level as it moves through time. The response trace is not intended to show a single fault or a literal recording. It shows the type of error that can arise when a system must reproduce a changing musical event while its electrical and mechanical conditions are unstable. Reducing the disturbance helps the response align more closely with the reference.

  • Musical reference
  • System tracking response
Illustrative signal-tracking plot. Frequency composition runs from left to right, amplitude rises vertically and time recedes across the plane. A solid musical reference changes its harmonic composition and amplitude as it moves through time; the dashed system response follows that changing spectrum with illustrative timing, amplitude and harmonic-profile error determined by Matrix insertion loss. Return loss changes the reflected field only. This is a conceptual illustration, not measured data.

Reading the two views together

The first plot answers a simple question: can the system stay with the music while its operating conditions are moving? It uses Distance to make the journey visible.

The second plot changes the viewpoint. Instead of following the route through the system, it shows how the music’s frequency composition and amplitude evolve through time. The musical reference becomes a changing profile. The system response follows beside it, with delay, level error and changes in spectral shape becoming visible as a difference between the two traces.

First plot: signal path Second plot: signal profile
A route through the system A view across frequency composition and time
Distance makes the journey visible Time makes the musical event visible
The moving field is the obstacle The difference between traces is the tracking error
“Can the dog keep up with the hare?” “What has changed in the music while it tries?”

A system problem needs system thinking

Different products address different routes by which disturbance can circulate.

The source of disturbance can be mains-borne, generated inside a component, carried by a cable, coupled through a chassis or transmitted mechanically from a loudspeaker. These routes interact. That is why Quiescent looks at mains control, component grounding, interconnects, speaker connection and amplification as parts of one connected environment.

Quiescent uses reflection and transmission control to manage unwanted high-frequency energy across those connected paths. Return Loss describes the reflected portion; Insertion Loss describes the reduction in transmission. Together, they help stabilise the conditions in which the existing components follow the musical reference.

From tracking error to the wider system

Tracking error describes the consequence: a system has more difficulty preserving the musical reference when its surroundings are unsettled. The following pages examine the mechanisms behind that condition — how unwanted energy can reflect at a boundary, continue through it, and affect a sensitive subsystem.

Each takes one part of the wider system view in turn.

Explore further

High-frequency behaviour

High-Frequency Propagation

How high-frequency energy behaves on cables and PCB tracks, and why wavelength, return paths and skin effect matter in audio systems.

Explore High-Frequency Propagation

Matrix boundaries

Return Loss

How a controlled boundary reduces the energy reflected back into the system.

Explore Return Loss

Matrix boundary

Insertion Loss

How a Matrix boundary reduces unwanted energy that would otherwise pass through and continue onward.

Explore Insertion Loss

Sources and further reading

The animations are conceptual illustrations of dynamic disturbance and signal tracking. Their visual separation is explanatory rather than a measured error level or audibility scale.

The engineering references explain interference control, connected paths and boundary behaviour. Quiescent’s own research and development informs their application to working audio systems. The industry references provide historical context for audio signal-comparison methods.

Engineering references

  1. Electromagnetic Compatibility Engineering — Henry W. Ott (Wiley, 2009). Grounding, cabling, filtering, shielding and RF interference control.
  2. Introduction to Electromagnetic Compatibility, 2nd edition — Clayton R. Paul (Wiley, 2006). Transmission lines, signal integrity, conducted and radiated interference, and system-level EMC.
  3. IEC 61000-4-6:2023 — Immunity to conducted disturbances induced by radio-frequency fields. An international reference for conducted RF disturbances.
  4. Rohde & Schwarz: Input Reflection Parameters. A practical introduction to reflection coefficient, S11 and return loss.

Industry context

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