Source-aware MP3 encoding for shellac, 78 rpm and historical disc transfers, with manufacturer replay-EQ context and guidance for choosing bandwidth after restoration.
For shellac and other historical discs, first establish the correct replay speed, stylus and equalisation. Only after a correct PCM transfer should you decide whether a narrower MP3 bandwidth is justified. Historical replay-EQ figures describe how the record should be played back; they do not directly tell you where to set the MP3 low-pass.
IASA's TC-04 guidance illustrates how varied electrically recorded coarse-groove discs can be. The figures below describe the replay equalisation needed to restore the intended tonal balance. They are included to show why a single “78 rpm curve” or one universal MP3 cutoff is inappropriate.
| Example | Bass EQ point | Treble replay characteristic | Treble reduction at 10 kHz |
|---|---|---|---|
| Capitol (1942) | 400 Hz | Correction begins around 2.5 kHz | -12 dB |
| Columbia (1925) | 200 Hz | Upper-frequency correction around 5.2–5.5 kHz | about -7 to -8.5 dB |
| Columbia (1938) | 300 Hz | Correction begins around 1.59 kHz | -16 dB |
| Decca (1934) | 400 Hz | Correction begins around 2.5 kHz | -12 dB |
| Decca/London FFRR (1949) | 250 Hz | Correction around 3 kHz with a 3 dB/octave slope | -5 dB |
| Victor (1938–47) | 500 Hz | Upper-frequency correction around 5.2–5.5 kHz | about -7 to -8.5 dB |
| Victor (1947–52) | 500 Hz | Correction begins around 2.12 kHz | -12 dB |
These are replay equalisation data, not encoder-cutoff recommendations. IASA also notes that published curves are not exhaustive and reputable sources can differ.
In historical disc literature, the LF turnover frequency is the point used to define the low-frequency part of the replay equalisation curve. The HF turnover frequency describes where the high-frequency replay correction begins, while figures such as -12 dB at 10 kHz describe how much treble attenuation the replay curve applies at that frequency.
These are equalisation parameters, not bandwidth limits. A disc with a 2.5 kHz HF turnover can still contain useful programme information well above 2.5 kHz. For MP3 encoding, first apply the correct replay EQ, then judge the actual useful bandwidth of the restored PCM before choosing a low-pass value.
lame.exe -V2 --lowpass 8 restored-78.wav access-copy.mp3lame.exe --abr 128 --lowpass 10 restored-disc.wav access-copy.mp3The numbers above are examples of the command structure only. An acoustic disc, an early electrical Columbia, a late FFRR pressing and an instantaneous broadcast transcription can have very different useful bandwidths. Measure the source rather than assigning a cutoff from the label name alone.
Disc rumble should normally be addressed before MP3 encoding. Although high-pass filtering can reduce rumble in principle, LAME's own high-pass implementation cannot reach the normal sub-100 Hz region at a 44.1/48 kHz sample rate. Use restoration/DSP tools for that stage, then use LAME to encode the cleaned PCM.
IASA TC-04 recommends documenting replay decisions and provides historical coarse-groove replay equalisation data, while warning that the table does not cover every curve and that research remains ongoing.