Should you trust listening tests or historical documents when identifying EQ curves — the difference in what each method can answer

Should you trust listening tests or historical documents to identify EQ curves?

Question answered on this page: When you want to know which EQ curve was used on a particular record, which is more reliable — listening and judging by ear, or researching historical documents?

The answer: two methods with different purposes

Listening tests and documentary research are both useful, but they answer different questions.

• Historical documents (patents, technical papers, the AES Journal, trade magazines, equipment manuals) tell you "what was intended and what was specified"
• Listening tests (switching between curves on a variable-EQ phono preamplifier and comparing by ear) tell you "what sounds most pleasing to the listener"

These two activities may look similar, but they are in fact answering different questions.

Why documents are better suited for identifying historical curves

For the factual question "which EQ curve was used to record this record?", documents provide more reliable evidence. Here is why.

Contemporaneity. Primary sources and patent documents from the period were written by people involved in the recording process, at the time the recordings were made. Patents documented the design specifications of cutting equipment, and trade publications (Billboard, High Fidelity, Audio Engineering) reported on curve transitions in real time.

Physical constraints of equipment. Equipment manuals specify which curves a given piece of equipment could produce. Recording with a curve that did not exist in the equipment's specifications was physically impossible without special modification.

Cross-referencing multiple independent sources. By comparing records left by people in different roles — engineers, executives, trade journalists — the biases in any single account can be mutually corrected.

Are listening tests suited for identifying historical curves?

Listening tests have several structural limitations when it comes to identifying the curve used in a recording.

Playback conditions. Playback volume, room acoustics, cartridge characteristics, amplifier characteristics, and many other elements of the playback environment affect what is heard. Even with the same record, changing the playback conditions can change which setting sounds "best."

It is worth noting that the effect of playback volume on perceived tonal balance may involve the influence of equal-loudness contours (such as those described by Fletcher and Munson) — the phenomenon whereby human hearing sensitivity varies by frequency at different volume levels. However, to my knowledge, no published literature has directly discussed the relationship between this effect and phono EQ curve selection.

Confirmation bias. Human judgment tends to be skewed toward confirming expected results. If one has a prior assumption that "this label should use this curve," one is more likely to judge that setting as sounding "good."

Reproducibility. The same listener, listening to the same record on a different day, may choose a different setting. Physical condition, mood, and music heard immediately beforehand can all influence the judgment.

An important caveat: comparing curves by ear is genuinely enjoyable

The point of this page is not that "listening is meaningless."

Enjoying a listening comparison and identifying a historical fact are different activities.

Switching between curves on a variable-EQ phono preamplifier and comparing how they sound is one of the pleasures of record playback. Listening with whatever setting sounds most pleasing to you is a matter of personal freedom.

However, equating "the setting that sounded most pleasing" with "the curve used at the time of recording" involves the structural problems described above.

In my view, keeping this distinction in mind is the key to resolving much of the confusion that surrounds discussions of EQ curves.

(→ Can you actually hear the difference when you change the EQ curve?)

Methodology of this series

In the blog series Pt.0–Pt.25, the author has adopted verification based on primary sources (technical papers, trade magazine articles, patents, equipment manuals, and engineers' testimony) as the fundamental methodology.

For details on this methodology → Pt.0

Related pages

• → Can you actually hear the difference when you change the EQ curve?
• → Why are there so many conflicting opinions about EQ curves?
• → Are there reliable references for EQ curves?

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