Why did phono EQ curves converge on the RIAA standard? A 100-year history from primary sources

The History of Phono EQ Curves

Your phono equalizer plays records according to a standard called "RIAA." But do you know why it's called "RIAA," or whether other standards ever existed?

Follow the thread, and it leads all the way back to the dawn of electrical recording in the 1920s. How did EQ curves — once different for every label and every era — converge into a single standard? That history is not as distant from today's record playback as you might think.

What kind of reader are you?

I want the big picture first (approx. 15–20 min)

What is an EQ curve, why was it needed, and how was it standardized? A century of history, condensed into three standalone parts.

→ Read the history in brief (In a Nutshell)

I'm looking for a specific answer (3–8 min per topic)

"What is the RIAA curve?" "How should I play pre-RIAA records?" Common questions answered one page at a time.

→ Browse the FAQ

I want all the details

The complete record of over two years of research. Written from primary sources — Bell Labs technical documents, patents, AES papers, and more — across 25 installments plus a prologue.

→ Overview and reading guide for "Things I learned on Phono EQ curves"

Recent updates

• May 16, 2026
  • ✏️ Are U.S. stereo LPs recorded with RIAA, or with per-label EQ curves? — Added Evidence 7 (design and owner's manuals of consumer stereo amplifiers, with tabulation from the August 1964 issue of Audio Magazine). Added the CSL test disc label to Evidence 3 and the Bell 3030 schematic to Evidence 7. Added AES E-Library links to Evidences 5 and 6
  • ✏️ What EQ curves were used before RIAA, and why were there so many — Added figures (the 1949 NAB vertical recording curve and the 1951 AES Standard Playback Curve)
  • ✏️ What was the Sapphire Group — the gatherings that broke down industry secrecy and paved the way for standardization — Added figures (1946 photo of the first Hollywood Sapphire Group meeting and the 1948 Audio Engineering article announcing the formation of the AES)
  • ✏️ When did the standards documents change their wording for the time constants from LCR to all-RC? — Added figures (the 1949 NAB standard's notes page and the Broadcasting Telecasting article reporting the 1953 NARTB revision)
  • ✏️ When was the RIAA curve established — years of pre-history leading up to January 29, 1954 — Added figures (the RIAA recording/reproducing curves graph and the 1953 Broadcasting Telecasting article on the momentum toward a recording-standard revision)
• May 15, 2026
  • ✏️ Can a playback EQ perfectly cancel a cutting EQ? — Adjusted the paragraph order at the start of §2
• May 13, 2026
  • 🔔 Newly published: Are LCR and RC phono equalizers fundamentally different?
  • 🔔 Newly published: Can a playback EQ perfectly cancel a cutting EQ?
  • ✏️ When did the standards documents change their wording for the time constants from LCR to all-RC? — Tidied up the Read further section, replacing placeholder references with sister FAQ links.
• May 11, 2026
  • ✏️ Rudy Van Gelder's cutting equipment and EQ curves — what the equipment records and his own testimony tell us — Separated "The 'RVG sound' is not about the EQ curve," "Measuring the 1958 Somethin' Else," and "The cutting EQ curve and sound shaping are separate matters" into a new FAQ Where is the RVG sound made? A 3-way LTAS of Somethin' Else. This FAQ now ends at the "Connection to the EQ curve debate" section with a pointer to the new FAQ

→ Past revision history

About this content

This section (this page, In a Nutshell, the FAQ, and Research Notes) was built on the content of the blog series, with Claude Code (Anthropic) used as an aid for structuring and drafting. Codex (OpenAI) is also used alongside Claude Code, as a sub-agent for close reading of primary sources. Responsibility for factual accuracy and final editorial judgment rests with the author.

→ How is generative AI used in producing this site?

The blog series (Pt.0–Pt.25) on the parent site was researched and written by the author over more than two years, drawing on primary sources — circuit diagrams, technical documents, academic papers, industry journals, patents, and more — examined by hand.

Wherever possible, "established facts" and "the author's interpretation or conjecture" are explicitly distinguished throughout the text.

Start with a popular FAQ

• What is the RIAA curve?
• Can you hear a difference when you change the EQ curve?
• How should I play pre-RIAA records?
• EQ curve vs. mastering — which determines the sound?
• Are all U.S. stereo LPs on the RIAA curve?