What EQ curves were used before RIAA, and why were there so many
What EQ curves existed before RIAA?
Question answered on this page: What EQ curves were used for record recording before the 1954 RIAA standardization? Why were there so many different curves?
Overview
Before the RIAA curve was established in 1954, recording and playback characteristics for records were not standardized. Each record company, broadcast network, and cutting studio used its own curve, tailored to its equipment and purposes.
Below are the major curves used in the United States. Each curve is described here in terms of its combination of time constants.
→ For the basics of EQ curves (time constants, turnover, bass shelf, rolloff), see What is phono equalization?
Major pre-RIAA curves
| Curve name | Used by | In use from | Shorthand | Turnover frequency (time constant) | HF time constant | Bass shelf time constant | Remarks |
|---|---|---|---|---|---|---|---|
| Orthacoustic | RCA/NBC | c. 1939 | 500B-16 | 500 Hz (318 μs) | 100 μs (±16 dB at 10 kHz) | 3,180 μs | For broadcast transcription discs. The prototype for the NAB standard |
| 1942/1949 NAB | Broadcasters | 1942–1953 | 500B-16 | 500 Hz (318 μs) | 100 μs (±16 dB at 10 kHz) | 3,180 μs | The first-ever recording standard. Adopted Orthacoustic virtually unchanged |
| Columbia LP | Columbia Records | 1948–1955 | 500C-16 | 500 Hz (318 μs) | 100 μs (±16 dB at 10 kHz) | 1,590 μs | For LPs. Bass boost characteristic differs from NAB |
| Old Orthophonic | RCA Victor | 1950–July 1952 | 500N-12.7 | 500 Hz (318 μs) | 75 μs + low-pass filter (±12.7 dB at 10 kHz) | None | For 78 rpm and early 45 rpm discs. No bass boost. Low-pass filter applied |
| AES | Academic society | 1951– | 400N-12 | 400 Hz (398 μs) | 64 μs (±12 dB at 10 kHz) | None | A playback curve proposed as a compromise among the various companies' curves |
| New Orthophonic | RCA Victor | August 1952– | 500R-13.7 | 500 Hz (318 μs) | 75 μs (±13.7 dB at 10 kHz) | 3,180 μs | Effectively identical to the later RIAA |
| ffrr (LP #1) | Decca (UK) | 1950–c. 1952 | 500N-FLAT | 500 Hz (318 μs) | None | None | Used on Decca's earliest LPs; same characteristics as their 78 rpm discs at the time |
| ffrr (LP #2) | Decca (UK) / London (US) | c. 1952– | 500N-10.5 | 500 Hz (318 μs) | 50 μs (±10.5 dB at 10 kHz) | None | Used by Decca (UK) until their transition to RIAA (c. 1957) and by London (US) until c. mid-1954. Widely influential on European pressings |
Note: The table above is simplified. Details of time constants and characteristics may vary between sources for some curves. Many additional curves existed that are not listed here, particularly those used in various European countries.
→ For the author's investigation of curves used by U.S. labels before RIAA, see blog post Pt.17
→ For the overall summary, see blog post Pt.25
Why were there so many different curves?
"If standardization would have been convenient, why did each company use a different curve?" is a natural question. The answer lies in the technical circumstances of the time.
Cutter heads did not have flat frequency response. In the pre-RIAA era, the cutter heads used for disc cutting had significant frequency response irregularities of their own. Recording engineers achieved their target recording characteristics by "combining" the cutter head's behavior with the recording equalizer. Different cutter heads required different equalizer settings, and variations in on-site practices may have led to variations in the resulting recording characteristics as well.
The high-frequency pre-emphasis trade-off. Stronger high-frequency pre-emphasis is beneficial for reducing noise on playback, but it increases distortion during recording. Where to strike this balance was left to the judgment of each company and each engineer, and this became one factor contributing to the differences among curves.
Different targets of "standardization." The 1942 NAB standard was intended for broadcast transcription discs; consumer 78 rpm records and LPs were outside its scope. So even within the "pre-standardization" era, the situation differed between broadcast and consumer contexts.
Distinguishing "pre-RIAA" from "pre-standardization"
The term "pre-RIAA" is convenient but requires care.
Even before the 1954 RIAA, the NAB standard for broadcasters had existed since 1942. It was not complete chaos — partial standardization had been progressing in stages.
On the other hand, for consumer records (78 rpm, LPs, and 45 rpm), no industry-wide binding standard existed before RIAA. Each company and cutting studio determined its own recording curve, and this was the primary reason for the diversity of curves.
→ In a Nutshell: from the birth of electrical recording to the NAB curve — a quick overview of the pre-standardization history
→ In a Nutshell: from the postwar period to the birth of the RIAA curve — from the LP's arrival to the RIAA
Can the "correct curve" be identified?
It is natural to want to apply the "correct playback curve" for pre-RIAA records. In practice, however, there are several difficulties.
- The label name alone may not be enough to identify the curve (even within the same label, curves could differ by period or cutting studio)
- "Recommended playback settings" listed in contemporary literature may not match the actual recording curve
- Multiple "recommended curve" lists may assign different curves to the same label
These issues are addressed in detail on the following pages.
→ How should I play pre-RIAA records?
→ When did each label switch to RIAA?
Related pages
- → When was the RIAA curve established? — timeline and background of its establishment
- → What is the RIAA curve? — definition and three time constants
- → Why did RIAA become the standard? — technical, political, and economic factors
- → The emergence of the Orthacoustic curve — blog post Pt.5 — the starting point of the pre-RIAA era
Revision History
- April 8, 2026: Initial publication