Overview and reading guide for the blog series Pt.0–Pt.25

Last updated: April 8, 2026

About the series "Things I learned on Phono EQ curves"

This series documents more than two years of research into the history of phono EQ curves, conducted from the summer of 2022 onward. Spanning 25 installments plus a prologue, it traces the story from the dawn of electrical recording in 1925 to the present day, drawing on primary sources throughout.

The investigation began with four questions:

Why do records need EQ curves at all?
How did the technology of each era realize those curves?
Why did curves remain inconsistent, and what did those differences mean?
How did research, development, and industry initiatives in the United States lead to a unified standard?

Sources consulted include circuit diagrams, technical documents, academic papers (AES Journal, etc.), trade publications (Billboard, Down Beat, etc.), patents, catalogs, and service manuals.

Reading guide

Reading straight through

Reading from Pt.0 (the prologue) onward traces the path to standardization from both technical and industrial perspectives. However, the series is extremely long (expect several hours), so starting with In a Nutshell (approx. 15–20 min) to get the big picture first is recommended.

Reading by topic

You can jump directly to any part from the list below. Each part stands on its own as an article, though some contain references to adjacent parts.

If you have a specific question, the FAQ may be the quickest route. Each FAQ page also links to the relevant parts.

Overview of each part

Pt.0 — Prologue: Why this investigation

What motivated this research. Premises and methodology.

→ Read Pt.0

Pt.1 — Constant amplitude and constant velocity: The physics of electrical recording

The commercialization of electrical recording in 1925. The principles of constant-amplitude and constant-velocity recording in the Western Electric rubber-line recorder. EQ curves were determined by the physical characteristics of the cutterhead, not by electronic circuits.

→ Read Pt.1

Pt.2 — The world's first electrical recordings and beyond

Electrical recording technologies beyond Western Electric. The Brunswick light-ray method.

→ Read Pt.2

Pt.3 — Recording technology developments in the 1930s

Independent technology development to avoid licensing fees. The Bramline system in Britain. Unintentional high-frequency pre-emphasis caused by microphone frequency response.

→ Read Pt.3

Pt.4 — Film soundtracks and transcription discs

33⅓ rpm transcription discs predated commercial 78 rpm records. Vitaphone and Sound-on-Disc. Vertical-cut transcription discs and the introduction of intentional high-frequency pre-emphasis.

→ Read Pt.4

Pt.5 — Stokowski, Bell Labs, and the birth of Orthacoustic

Stokowski's contributions to Bell Labs / Western Electric experimental recordings. NBC=RCA lateral-cut transcription discs. The origins of the Orthacoustic characteristic in 1941.

→ Read Pt.5

Pt.6 — Lacquer discs, acetate recorders, and stylus pressure

The spread of lacquer discs and acetate recorders. Pierce & Hunt's research on stylus pressure and playback distortion. Demonstration that lateral-cut recording was superior in terms of harmonic distortion.

→ Read Pt.6

Pt.7 — The era of the piezoelectric pickup

The piezoelectric (crystal) cartridge, introduced in the late 1930s for jukeboxes. Its decades-long dominance in consumer equipment. Attempts at constant-amplitude recording systems and their failure.

→ Read Pt.7

Pt.8 — The 1942 NAB standard

The NAB (National Association of Broadcasters) established standards for broadcast transcription discs. How NBC=RCA Orthacoustic was selected. Wartime constraints limited the specification to 16 items.

→ Read Pt.8

Pt.9 — Wartime and postwar playback conditions, and the US–UK divide

The reality of playback equipment during and after the war. Britain's cautious stance on high-frequency pre-emphasis. The proliferation of independent EQ curves in the United States. An era when noise reduction took priority over standardization.

→ Read Pt.9

Pt.10 — The 1949 NAB standard

Completion of the 1949 NAB standard. The technical debate over the strength of NAB's high-frequency pre-emphasis (100 μs).

→ Read Pt.10

Pt.11 — The arrival of the Columbia LP microgroove

June 18, 1948: the Columbia LP announcement. Secret development from around 1939. Multiple claimants to credit, with conflicting accounts.

→ Read Pt.11

Related FAQ: Who invented the LP?

Pt.12 — The Columbia LP recording curve

The technical background of the Columbia LP recording curve. The only difference from the NAB curve was the bass shelf time constant. Hot stylus technology (a Columbia monopoly for 1–2 years). Advances in cutting capability above 10,000 Hz.

→ Read Pt.12

Pt.13 — The arrival of the RCA Victor 45 rpm

January 10, 1949: the RCA Victor 45 rpm announcement. The lineage of the old Orthophonic curve. The beginning of the "Battle of the Speeds."

→ Read Pt.13

Pt.14 — The Battle of the Speeds and its resolution

The industry's response in 1949–1950. The final settlement: LPs for albums, 45 rpm for singles.

→ Read Pt.14

Pt.15 — The history of the term "High Fidelity"

"High Fidelity" originated in 1927. Postwar technical debates over its definition. Its spread as a marketing term in the LP / 45 rpm era.

→ Read Pt.15

Pt.16 — The Sapphire Group, AES, and the momentum toward standardization

From industry secrecy to cooperation. The roles of Audio Engineering magazine and AES. The development of the AES reproducing curve.

→ Read Pt.16

Related FAQ: What was the "Sapphire Group"?

Pt.17 — Recording characteristics by label, 1949–1953

The separation of recording studios and cutting studios through the spread of magnetic tape. The introduction of the Pultec EQP-1A. Matrix-number-based investigation methods. RCA Victor's adoption of New Orthophonic in August 1952 (the precursor to RIAA).

→ Read Pt.17

Pt.18 — The establishment of the NARTB, AES, and RIAA standards

June 1953: NARTB approval. December 1953: AES draft approval. January 29, 1954: RIAA Standard Recording and Reproducing Characteristic approved. June 1954: AES TSA-1-1954 formally approved. The composition of the RIAA Technical Committee (chief engineers from five major labels). The selection of 75 μs (identical to RCA Victor New Orthophonic). The introduction of the feedback cutter and the realization of flat response.

→ Read Pt.18

Pt.19 — Disc recording equipment of the 1950s–1970s

The evolution of recording EQ: from standalone EQ units to circuits built into amplifiers. Analysis of systems by Gotham, Fairchild, Westrex, Neumann, and Ortofon. RIAA equalization realized within amplifiers.

→ Read Pt.19

Pt.20 — How the RIAA transition actually unfolded

Early adoption by RCA Victor and Capitol. Columbia's transition in the summer of 1954 (completed in roughly one year). Estimated near-complete adoption by the end of 1955. Methods for investigating each label's transition timing, and the construction of curve tables based on technical documents and matrix data.

→ Read Pt.20

Pt.21 — Test records and EQ curves

Records of frequency response measurements for 78 rpm and 33⅓ transcription discs. Feedback cutter era specifications (RIAA below 1 kHz, constant velocity above). The 1953 Dubbings and 1954 Folkways exceptions.

→ Read Pt.21

Pt.22 — Consumer amplifier phono EQ, 1957–1964

In the early stereo era, some amplifiers still offered non-RIAA EQ selections. The McIntosh exceptions (C-22, C-24, MA230). The establishment of the premise that stereo = RIAA playback.

→ Read Pt.22

Pt.23 — RIAA deviation measurements and LCR / CR filters

RIAA deviation measurement data from the 1972 Stereo Sound magazine survey. The LCR vs. CR filter debate. The Bell Labs / Westrex lineage. The postwar dominance of RC circuits in consumer playback.

→ Read Pt.23

Pt.24 — From microphone to final medium: The full signal chain

Multi-stage sound shaping across recording, mastering, and playback. Active equalization practices in popular music. The limitations of identifying curves by ear.

→ Read Pt.24

Pt.25 — Conclusion: What I learned

A chronological summary of what was learned in Pt.0–24. Current conclusions. References and acknowledgments.

→ Read Pt.25

Revision History

April 8, 2026: Initial publication