What EQ curves were used on 1948–1958 mono LPs — why there is no single right answer
What EQ curves were used on mono LPs from 1948 to 1958?
Question answered on this page: During the monaural LP era before RIAA unification (1948–1958), what EQ curves did each label use for recording?
The honest answer: there is no single right answer
From the introduction of the LP in 1948 through the establishment of the RIAA standard in 1954 and the completion of the transition afterward, each label used a different curve. Moreover, even after RIAA was established, the transition took one to two years to complete.
Therefore, there is no single answer of the form "mono LPs use this curve." What follows is a label-by-label overview based on verifiable sources.
Approximate timeline by label
| Label | Transition to RIAA (or equivalent) | Curve used before transition |
|---|---|---|
| RCA Victor | From around August 1952 (New Orthophonic = identical to RIAA) | Old Orthophonic |
| Capitol | From around fall 1953 | AES |
| Columbia | Estimated completion in early 1955, late 1955 at the latest ("less than half transitioned" as of August 1954 — Billboard) | Columbia LP |
| Mercury | Around late 1954 | AES |
| U.S. Decca | Around early 1955 | NAB |
| MGM | Around late 1954 | Likely 500N-12 (Old Orthophonic turnover/bass shelf + AES HF rolloff), though accounts vary |
| London (UK Decca) | Early 1954 | ffrr |
| Westminster | Same as Columbia (cutting outsourced to Columbia) Some outsourced to RCA Victor |
Columbia LP Old/New Orthophonic (jacket states AES) |
This table is an overview and does not guarantee the recording curve of any individual pressing. For details on each label → When did each label switch to RIAA?
Why it is not straightforward
Several factors make playback of transition-era records complicated.
Continued use of stampers. Even after a label switched to RIAA, stampers cut with the old curve continued to be used for pressing until they wore out. Records with the same catalog number may have been cut with different curves depending on the pressing date.
Outsourced cutting. Labels without their own cutting facilities outsourced to majors such as Columbia, RCA Victor, and Capitol. The outsourcing facility's equipment and transition timeline applied directly, so the label name alone is not enough to determine the curve.
Absence of records. For many recordings, no accurate record of the EQ curve used has survived. The table above also includes estimates based on trade journal articles and engineer testimonies.
Practical guidelines
Even without a single right answer, there are practical approaches.
1. Start by listening with RIAA. Most curves used during the transition period share the same turnover frequency as RIAA (500 Hz); the differences lie mainly in the bass shelf and high-frequency pre-emphasis. Starting with RIAA and using it as a baseline is practical.
2. If something sounds off, try the label's pre-transition curve. Using the table above as a reference, try a curve with a lower turnover if the highs sound harsh, or a gentler rolloff if the bass sounds thin.
3. Remember that "the setting that sounds preferable" and "the setting used in recording" are separate questions. Even if changing settings on a variable-EQ phono equalizer produces a "better" sound, that does not necessarily mean it matches the curve used in recording (→ Can you hear a difference when you change the EQ curve?).
If you are considering a variable-EQ phono equalizer: → Do I need a variable-EQ phono equalizer?
For reliable curve references: → Is there a reliable EQ curve reference?
Revision History
- April 8, 2026: Initial publication