Are U.S. stereo LPs recorded with RIAA curves, or with per-label EQ curves? What do label-by-label curve charts actually show? Answered from cutting system design and engineers' own testimonies.

Are all U.S. stereo LPs recorded with RIAA curves?

Question answered on this page: Were all U.S. major-label stereo LPs recorded with RIAA curves after 1958? Or were different EQ curves used by different labels?

Introduction: two different acts

Before getting into the subject, there is an important distinction to make.

• Switching curves and comparing sounds to find your preference — this is one of the pleasures of record playback. Listening with the sound you prefer is a personal choice.
• Identifying that "this record was recorded with XX curve" — this is a separate act that requires historical and technical verification.

This page deals with the latter: which curve was in fact used for recording.

Answer: U.S. stereo LPs were recorded with RIAA curves

Stereo LPs by major U.S. labels since 1958 have been recorded with RIAA curves.

This is confirmed by multiple independent lines of evidence.

Evidence 1: design of stereo cutting equipment

When stereo LPs were introduced to the U.S. public in 1958, the entire recording system used for cutting in the United States (the stereo cutter head and recording amplifier combination) was designed with RIAA recording characteristics as the standard.

To produce stereo LPs, it was necessary to install this new cutting equipment. In other words, the entire recording system was updated to an RIAA-based design at the point when stereo LPs were produced.

This is also confirmed by technical papers written by the equipment developers themselves. Regarding the Westrex 3A stereo recording system, which played a central role in the 1958 stereo disc standardization, its developers C.C. Davis and J.G. Frayne wrote the following in The Westrex Stereodisk System (IRE paper, 1958):

"the input network of the recording amplifier provides the RIAA reproducing equalization."

The same paper further states explicitly that, in commercial cutting practice, the RIAA recording pre-emphasis characteristic is added to this:

"This characteristic is modified in commercial practice by inserting the RIAA or equivalent recording pre-equalization characteristic."

In other words, the Westrex 3A was designed from the outset with RIAA in mind, and was not designed to accommodate other EQ curves.

To cut a stereo disc with a curve other than RIAA would have required special measures to deliberately circumvent the equipment design, and no record of such measures has been found.

(→ See Pt.19)

Primary source: C.C. Davis and J.G. Frayne, "The Westrex Stereodisk System," Proceedings of the IRE, Vol. 46, No. 10, pp. 1686–1693, October 1958.

Evidence 2: cutting engineers' testimonies

Several cutting engineers have testified that RIAA curves were used in their own facilities.

• A mastering engineer at Capitol testified: "Capitol's mastering used RIAA curves. That's all."
• A cutting engineer at Decca (UK) (1957–1972) testified: "There is no such thing as the FFSS curve. FFSS is a marketing term; Decca used RIAA."
• A mastering engineer at Columbia reported, after inquiring with senior engineers, that "the switch to RIAA was completed for all releases by 1955."
• Another veteran mastering engineer at Columbia testified: "Absolutely, positively, no Columbia curve was used in the stereo era."

(→ See Pt.20)

Evidence 3: Columbia's internal documents

An internal document prepared by William Bachman, Columbia's Director of Electronics and Research, has been discovered. This document contains the following:

• A graph showing the similarity between the Columbia curve and the RIAA curve
• A note that manufacturing variation was greater than the difference between the two curves
• A statement that "the RIAA curve is ideal for reproduction of Columbia LPs, and a gradual transition to RIAA should be implemented"

The document is undated, but has been identified as having been filed between the 1955 and 1956 memos.

Also, an article in the August 28, 1954 issue of Billboard reported that at that time less than half of Columbia's mastering equipment had been converted to RIAA, and that it would take another six months to complete the transition of all equipment.

Meanwhile, the CSL (Columbia Standard Level) test disc, distributed by Columbia to radio stations beginning in February 1955, bears the label inscription: "Columbia Standard Characteristic: as per R.I.A.A - N.A.R.T.B. industry norm."

These indicate that Columbia's transition to RIAA was completed in the first half of 1955, or at the latest in the second half of 1955.

Evidence 4: Rudy Van Gelder's equipment records

Rudy Van Gelder's studio, which handled recording and cutting for jazz labels such as Blue Note, Prestige, and Impulse!, introduced RIAA recording equipment (Gotham PFB-150WA) in early 1955.

Van Gelder himself stated his use of RIAA characteristics in an article he contributed in October 1955.

Blue Note and Prestige records differ only in label artwork; cutting was all done in the same Van Gelder studio, using the same equipment.

(→ See Pt.19)

(→ Rudy Van Gelder's cutting equipment and EQ curves)

Evidence 5: the 1957–1958 stereo disc standardization process

The selection of the stereo disc standard was not a unilateral decision by any single company or country. It was a consensus-building process in which engineers from the U.S. and Europe held repeated meetings throughout 1957 and 1958. H.E. Roys, who served as chairman of the RIAA stereo disc standards committee, documented this process in detail in his retrospective paper The Coming of Stereo (JAES, 1977).

The main milestones were as follows:

• September 5, 1957 — Westrex held a public demonstration of its 45/45 system for industry representatives in New York
• November 28, 1957 — A European meeting in Zurich, where European engineers also agreed to support the 45/45 method
• December 17–18, 1957 — RIAA met in Indianapolis and discussed adopting the 45/45 method
• January 21, 1958 — The EIA (Electronic Industries Association) approved the technical specifications for the 45/45 method
• March 25, 1958 — The RIAA Board officially approved the 45/45 stereo disc standard. William Bachman of Columbia put forward the motion to approve
• March 27, 1958 — The EIA gave its final approval

Of particular note are the words attributed to Arthur Haddy of Decca (UK) at one of these meetings:

"Roys, it does not matter which system we choose, we must have one and only one system."

This standardization process proceeded with RIAA as the assumed equalization characteristic for stereo as well. Continuing to use the RIAA curve — already established for monaural LPs — was the implicit premise, and there was no discussion of adopting a separate EQ curve for stereo.

The fact that William Bachman of Columbia was the one to put forward the approval motion at the RIAA Board is also indirect evidence that Columbia itself had completed its transition from the Columbia LP curve to RIAA before entering the stereo era (→ Evidence 3).

Primary source: H.E. Roys, "The Coming of Stereo," Journal of the Audio Engineering Society, Vol. 25, No. 10/11, pp. 824–827, October/November 1977.

Evidence 6: professional stereo-era playback equipment was also designed around RIAA

Evidence 1 through 5 above all concern the recording side (cutting equipment, engineers, internal documents, the standardization process). What about the playback side?

The Fairchild 605, released in 1960, is a professional stereo phono equalizer amplifier designed for broadcast stations, studios, and mastering rooms. Its designer, Erling P. Skov, described its EQ positions in Equalized Stereo Preamplifier for Professional Use (JAES, 1960) as follows:

"RIAA is the standard equalization for stereo records, 3,180, 318, and 75 μsec; flat is RIAA minus the treble attenuation; and roll-off is RIAA with an additional 40-μsec roll-off."

In other words, the three EQ positions provided by the Fairchild 605 were:

• RIAA — the standard
• Flat — RIAA minus the treble attenuation (a derivative defined relative to RIAA)
• Roll-off — RIAA with an additional roll-off (also a derivative defined relative to RIAA)

All three are configurations organized around RIAA as the reference. There are no positions for older EQ curves such as Columbia LP, AES, NAB, or ffrr.

In 1960, a designer of professional equipment stated outright that "RIAA is the standard equalization for stereo records," and built the EQ structure of his product around RIAA. This indicates that the stereo-era playback environment was also operated with RIAA as the common reference.

Both the recording side (Evidence 1–5) and the playback side (Evidence 6) of the stereo era can be confirmed, from primary sources on equipment design, to have been designed and operated with RIAA as the common reference.

Primary source: Erling P. Skov, "Equalized Stereo Preamplifier for Professional Use," Journal of the Audio Engineering Society, Vol. 8, No. 4, pp. 250–253, October 1960.

So why does the "non-RIAA curve" theory exist?

On the other hand, there is also a claim in circulation that "most U.S. stereo LPs are recorded with non-RIAA curves." The following summarizes the typical arguments offered for this claim.

1. Judgments based on aural comparison

When you switch curves on a variable-EQ phono equalizer, the sound changes. And sometimes one setting sounds "better" than another.

However, changing the EQ curve is a change in frequency response and phase response. It is physically natural for the sound to change, and "the sound changed" does not mean "the recording curve has been identified."

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

2. "Recommended curve" lists by label

Several tables on the Internet assign the "correct EQ curve" to each label. However, comparing these tables reveals cases where different curves are recommended for the same label.

For example, one table recommends "AES" for a given label, another recommends "NAB," and yet another recommends "Columbia."

If these tables were based on objective measurements, the recommendations for the same label should match. The fact that they disagree suggests that these tables reflect subjective choices based on aural preferences.

3. Confusion between "recommended playback settings" and "recording curves"

The "recommended settings by label" lists that appeared in 1950s magazine articles were guides to recommended settings on the playback side (in effect, "it is easier to listen with these settings"). They were not records of the curves used at the time of recording. There are cases where these two have been confused.

4. The implicit assumption that "label = curve"

Label-specific curve lists rest on the premise that once you know the label, you know the curve. However, a record's EQ curve is determined during the cutting process — specifically, by the recording system (cutter head and recording amplifier combination) used for cutting.

Not every label owned its own cutting facilities. Outsourcing cutting and pressing was common, and the actual production process cannot be captured by a simple "label = curve" correspondence.

• Blue Note and Prestige records were both cut at Rudy Van Gelder's studio, using the same equipment, by the same engineer (different labels sharing the same studio, equipment, and engineer)
• Contemporary and Good Time Jazz initially outsourced cutting and pressing to the Charles Eckart Company, but later their in-house engineer Roy DuNann took over cutting himself, with only pressing outsourced to the Capitol LA plant or the RCA Victor Hollywood plant (the same label changing its cutting arrangements over time)
• Mercury Living Presence had its records cut at Fine Sound Studios or Fine Recording, while pressing was outsourced to the RCA Victor Indianapolis plant or Richmond Record Pressings plant (cutting and pressing performed at separate facilities)

If "each label had its own curve," then Van Gelder would have had to change his equipment settings every time he switched between Blue Note and Prestige sessions.

On the other hand, major labels like RCA Victor and Columbia, which operated cutting facilities across the country, had established internal practices to maintain near-uniform quality regardless of which facility performed the cutting. While results were not always identical — cutting engineers differed in skill and taste — at the very least, the EQ curve standard was unified within the company. And that standard was RIAA (→ Evidence 3).

Furthermore, stereo-era disc recording equalizers had fixed characteristics, aside from a calibration position (treble pre-emphasis only OFF), and changing the curve was not straightforward. Even if a change were possible, it would require test cutting and measurement each time to verify that the change was correctly applied. No record of such work being performed every time the label changed is known to the author (at least, the author has been unable to confirm any).

What determines the EQ curve is not the label name but the equipment used for cutting. And stereo-era cutting equipment was designed with RIAA as the standard (→ Evidence 1).

Supplement: what this page does not claim

This page does not negate the following points.

• It is historical fact that multiple EQ curves existed during the pre-RIAA period (before 1954). Before RIAA was established, each label used its own curve (→ The History of Phono EQ Curves: In a Nutshell)
• During the monaural LP transition period (1954–1958), some records may have remained on non-RIAA curves. The timing of transition varied, especially among independent studios (→ When did each label switch to RIAA?)
• It is physically natural that changing the EQ curve changes the sound.
• Listening with the sound you prefer is a personal choice.

Summary

That U.S. stereo LPs (1958 onward) were recorded with RIAA curves can be confirmed by multiple independent lines of evidence: the design of the cutting equipment, engineer testimonies, internal company documents, equipment records, the industry-wide standardization process, and the design of professional playback equipment.

As for the claim that they were recorded with non-RIAA curves, the author has not so far been able to confirm any presentation of grounds drawing on primary sources (recording equipment specifications, cutting engineers' testimonies, or label technical documents). Aural comparison appears to be the principal basis offered.

Switching curves and comparing sounds is one of the pleasures of record playback, but "what sound do you prefer" and "what curve was used in the recording" are two different questions. We hope this page helps in making that distinction.

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