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 18, 2026
  • ✏️ How should pre-RIAA records be played on modern equipment — sorting out practical options — Added figures (Pilot SP-210 (1959) front panel, Esoteric Sound Re-Equalizer)
  • ✏️ Why did the U.S. and Europe use different EQ curves — the divergence in turnover frequencies and its background — Added figures (Fig. 5 of H.H. Scott 1954 — basic makeup of common reproducing curves; Decca ffrr curve from Wireless World, October 1954)
  • ✏️ Do you need a variable-EQ phono equalizer? — decision criteria by collection type — Added figure (FM Acoustics FM 122-MKII Phono Linearizer)
  • ✏️ What factors besides the EQ curve affect the sound of a record — an overview of the signal chain from recording to cutting — Added figure (Pultec EQP-1A variable equalizer)
  • ✏️ Can a playback EQ perfectly cancel a cutting EQ? — Added quotes in §5.1 from Lipshitz et al.'s 1980 preprint caution and the 1983 Shanefield comment with authors' reply, and in §4 from Lipshitz et al.'s 1980 preprint on cutter head / cartridge minimum-phase behavior
• May 17, 2026
  • ✏️ Why did the 1942 NAB standard use a ±2 dB tolerance curve, not time constants? — Added figure (lateral recording characteristic from the 1949 NAB standard)
  • ✏️ What EQ curve should you use for 78 rpm records — an honest look at an open question — Added figure (Bernards 1944 booklet explaining 'flat' electrical recording)
  • ✏️ Should you trust listening tests or historical documents to identify EQ curves? — Added figure (Westrex 2A feedback recorder frequency response from Yenzer 1949)
  • ✏️ What EQ curves were used on 1948–1958 mono LPs — why there is no single right answer — Added figures (Mercury MG-50000 rear cover with AES + Capitol SAL-9020 booklet playback curve)
  • ✏️ What a 46-issue close reading of 'Dialing Your Disks' (1950s High Fidelity) reveals — Added figure (close-up of Prestige PRLP-200 back cover with the RIAA curve marking)

→ 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?