Are there reliable references for EQ curves — research-based resources and criteria for evaluating source reliability

Are there reliable references for EQ curves?

Question answered on this page: When researching the EQ curves used by different labels, are there reliable references? What criteria should you use to judge the reliability of a source?

The answer: no perfect chart exists, but research-based resources do

There is no perfect chart that definitively lists "this label used this curve." However, several resources based on systematic research do exist and are reasonably reliable.

At the same time, sources that do not disclose their evidence are also in circulation. Below, I present recommended resources and criteria for judging source reliability.

Recommended research-based resources

James R. Powell, Jr., "Audiophile's Guide to Phonorecord Playback Equalizer Settings" (ARSC Journal, 1989)

This paper was published in the journal of the Association for Recorded Sound Collections (ARSC). It systematically surveys the EQ curves used on pre-RIAA records, drawing on technical documentation. The methodology is clearly stated, and the supporting sources are cited.

PsPatial Audio website

The website of PsPatial Audio (Alastair MacMaster and Richard Brice), the developers of Stereo Lab software for Mac, features a wide range of content on the history of recording technology. Their discussion of disc EQ curves is grounded in objective sources such as published papers, circuit diagrams, and equipment manuals. They also offer a PDF listing recommended playback curves by label.

Audacity Wiki: "Playback equalization for 78 rpm shellacs and early 33⅓ LPs"

This page on the Audacity plugin site provides a comprehensive list of playback EQ curves for 78 rpm shellac records and early LPs. It references past resources including the Powell paper and PsPatial mentioned above, clearly cites its sources and rationale, and lists multiple candidate curves side by side where sources disagree. The fact that it continues to be actively updated is a significant strength.

Manufacturer equipment manuals

Manuals for cutting equipment and phono equalizers from manufacturers such as Gotham, Westrex, and Fairchild include the EQ curve settings supported by each unit. Because this information is based on the physical specifications of the equipment, there is little room for subjective interpretation.

Contemporary trade publications

Trade magazines such as Billboard, High Fidelity, and Audio Engineering (later Audio) reported on EQ curve transitions in real time during the 1950s. These are valuable primary sources for determining when a particular label switched to RIAA.

Test records as a resource

Professional frequency-response test records used in cutting studios are also a valuable resource. Labels and equipment manufacturers produced test records to verify their own recording characteristics, and the characteristics documented on these records provide clues to the settings actually used in studios at the time.

(→ When did each label switch to the RIAA curve? — this page also discusses evidence of RIAA transitions drawn from test records)

For details → Pt.21

Criteria for judging source reliability

Numerous sources on EQ curves exist, but their reliability varies widely. The following criteria can help you evaluate them.

Are the sources cited? Reliable resources disclose their own evidence. When a resource states which documents it used to identify a given curve, readers can verify those underlying sources for themselves. When no sources are cited, there is no way to confirm where the information came from.

Is the methodology explained? Whether the author describes how the curves were identified — through documentary research, listening comparisons, or measurements — is an important indicator of reliability.

Does the claimed precision match the precision of the original sources? For example, some resources assign a specific curve name to a 1930s label with apparent certainty, yet the contemporary sources themselves may only state something like "turnover in the range of 200–300 Hz." When a resource claims greater precision than its underlying sources support, the basis for that claim warrants scrutiny.

Is there consistency across multiple sources? When comparing several resources on the same label and the same period, whether they recommend the same curve is an important piece of evidence. If different resources recommend different curves for the same label, there is a possibility that those recommendations are not grounded in objective evidence.

Summary

When searching for EQ curve references, keep in mind that a "chart matching label names to recommended curves" is not necessarily factual. Choosing resources that cite their sources and explain their methodology is the basic guideline for reaching reliable information.

For details → Pt.20, Pt.21

Related pages

• → How should I play pre-RIAA records?
• → Why are there so many conflicting opinions about EQ curves?
• → What curve should I use for 78 rpm records?
• → What EQ curves were used on mono LPs from 1948 to 1958?

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