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

• June 2, 2026
  • ✏️ Rudy Van Gelder's cutting equipment and EQ curves — what the equipment records and his own testimony tell us — Added the full term ("long-term average spectrum") at the first mention of "LTAS".
  • ✏️ Where is Rudy Van Gelder's "sound" actually made? — Recording- and mastering-stage sound shaping — Added the full term ("long-term average spectrum") at the first mention of "LTAS".
  • ✏️ What cutting curve did Rudy Van Gelder use before installing his Gotham (1953 to early 1955)? — Added the full term ("long-term average spectrum") at the first mention of "LTAS". Rewrote the "Current confidence and remaining means of verification" bullet list to separate pre-Gotham and Gotham-era points and to give context to the "AES at Hackensack" mention. Replaced the example for the earliest deadwax-traceable RVG cut from PRLP-142 to PRLP-180, and added the criteria used to identify RVG cuts on Prestige 10-inch LPs.
• June 1, 2026
  • ✏️ A 3-way LTAS of three Somethin' Else CDs — confirming the processing newly added at the RVG Edition 1999 stage — Split off the recording- and mastering-stage sound shaping (Hoffman's interpretation, LD+3 memo, JazzWax interviews) into a new FAQ Where is the RVG sound made? Recording- and mastering-stage sound shaping. This FAQ now focuses on the 3-way LTAS measurement case study of the 1958 Somethin' Else recording
  • ✏️ How did listeners actually play records before RIAA unification — casual listeners, audiophiles, and professionals — Added figure (Broadcasting Telecasting, May 23, 1955, p.134, Gotham PFB-150WA new product announcement)
  • ✏️ How generative AI is used in producing this site — what AI handles, and what it does not — Noted that Claude Opus 4.8 and 4.7 are currently used in parallel as a trial
  • ✏️ What sources did I use for this research? — an overview of primary sources over two years — Added "Analog Record Playback" by yosh to the Online articles section
  • ✏️ Rudy Van Gelder's cutting equipment and EQ curves — what the equipment records and his own testimony tell us — Split the related FAQ "Where is the RVG sound made?" into two pages: "Where is the RVG sound made? Recording- and mastering-stage sound shaping" and "Somethin' Else 3-way LTAS — measuring the processing newly added at the RVG Edition stage". The pointer at the end of the "Connection to the EQ curve debate" section in this FAQ has been updated to point to both. Rewrote the "Before Grampian / Gotham (1953 to early 1955)" section to be more neutral, splitting the detailed discussion off into a new FAQ "What cutting curve did Rudy Van Gelder use before installing his Gotham (1953 to early 1955)?"
  • ✏️ Where is Rudy Van Gelder's "sound" actually made? — Recording- and mastering-stage sound shaping — Split off from the FAQ Somethin' Else 3-way LTAS as a standalone FAQ covering the recording- and mastering-stage sound shaping (Hoffman's interpretation, LD+3 memo, JazzWax interviews). The concrete measurement case study lives in the related FAQ.
  • 🔔 Newly published: What cutting curve did Rudy Van Gelder use before installing his Gotham (1953 to early 1955)?

→ 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?