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Playback equalization for 78 rpm shellacs and early 33⅓ LPs

The audio on almost every phonograph record is not the same as that originally performed. For technical reasons the signal's frequencies need to be modified when cutting the disc. Playback equalization (EQ or de-emphasis) is necessary to restore the signal's original frequencies. Only thus can music lovers enjoy the original sound of the music performed long ago from their rare discs.

Usage

The most relevant EQ curves are presented as Table 1:
Which EQ curve will be needed for a specific record label is answered:

Using EQ curves in Audacity

Once converted to txt, you can import the curve in the Filter Curve EQ or Graphic EQ effects, by clicking Presets & settings -> Import....

Equalization (EQ) Curves explained

When phonograph records are made, the sound being recorded is deliberately distorted by reducing the volume of the low frequencies and increasing the volume of the high frequencies. This process, known as 'pre-emphasis', allows the low frequencies to be accommodated in the limitations of the record groove and reduces the effect of high frequency surface noise. If pre-emphasis was not carried out, the bass notes in the music would create a groove in the record that oscillated so wildly that the stylus could jump out of it on playback, and the treble notes would be drowned out by the surface noise of the stylus in the groove.
On playback, the pre-emphasis must be reversed in order to restore the original sound. This is known as 'de-emphasis' or equalization (EQ).
Modern vinyl records use a method of pre-emphasis and de-emphasis adopted by the Recording Industry Association of America (RIAA) in the 1950's, and the EQ curve used is known as the RIAA curve. However, before the RIAA curve was adopted, each record label used its own EQ curve for recording and, for these records (78rpm and early vinyl), the correct EQ curve must be used for playback.
Each EQ curve is a combination of two filter characteristics; a bass boost curve, defined by a 'Bass Turnover' (or 3dB) frequency, and a treble cut curve, defined by a '10 kHz Gain Roll-off' parameter, i.e. a defined level of treble cut at 10 kHz.
As an example, Figure 1 below shows the characteristic of the bass boost curve defined by a 500Hz Bass Turnover, and Figure 2 shows the characteristic of the treble cut curve defined by a 10 kHz Gain Roll-off of -13.7dB. These two curves, when combined, give the characteristic shown in Figure 3.\
Figure 1. Bass Boost curve: 3dB at 500 Hz
Figure 2. Treble Cut curve: -13.7 dB at 10 kHz
Figure 3. Combined Bass Boost and Treble Cut curve
The EQ curve may also include a Low Frequency Shelving filter, (although it is absent from the definition of most 78 rpm EQ curves). This addition reduces the effect of the bass boost at very low frequencies (typically 50 or 100 Hz) in order to attenuate low-frequency noise such as turntable rumble. Figure 4 shows the effect of a 50 Hz LF shelving filter being added to the curve in Figure 3. This is in fact the RIAA standard EQ curve.
Figure 4. Combined Bass Boost, Treble Cut and 50 Hz LF Shelving curve
Acoustically recorded (pre-electric) 78 rpm records have a completely different characteristic because they were cut with a different type of cutter (For more details see: Acoustic recordings). In some early EQ curves of electrically recorded shellacs, while there is a bass boost curve, there is no treble cut necessary – i.e. the 10 kHz gain roll-off is zero.
Note that in the combined EQ curve, the gains at the Bass Turnover frequency and at 10 kHz may be different from those specified by the parameters. This is not an error, but is due to fact that the gains of the bass boost and treble cut curves are simply added together.
Because 78 rpm EQ curves were non-standard and, in many cases, accurate records were not kept to show what EQ curves were used when recording 78s, there is a degree of uncertainty about what is the correct playback EQ for many record labels. The tables below have been obtained from websites which, in their turn, have compiled data from a number of sources and should prove reasonably accurate. However, the ear of the listener is the final arbiter - if it doesn't sound right, it isn't right!
According to NAB standards, the nominal speed of a 78 rpm record is precisely 78.26 rpm +/- 0.3% (for North America and other countries with an utility frequency of 60 Hz). According to British Standards Institution it is 77.92 rpm +/- 0.5% (for Britain, Europe and other countries with a mains frequency of 50 Hz).

EQ Curves

Pre-equalization of most records – especially of shellacs – was always determined by the cutter head used and often by internal regulations of the record company. Both left quite some room for the recording engineer to make changes to improve the sound. Also if Graumann uses 250 Hz in playback of an EMI disc and Copeland votes for 300 Hz this is not a contradiction. Both mean the same EQ curve but have different opinions on what sounds best. This should encourage you to try both versions and take the one which sounds right to your ears.
Please do not worry about fractions of a dB! Still in the 1960s an accuracy of a curve of +/- 2 dB was considered to be standard. In the 1950s +/- 3 dB were a very fine result and nobody will ever know if recording engineers in the 1940s or 1930s applied their curves correctly (or if they applied them at all!) So the spread in pre-equalization during recording will outnumber any bias in playback equalization by far.

Table of EQ Curves

The most relevant EQ curves are presented in Table 1. All curves are described from the point of view of a playback or de-emphasis curve, where bass / low frequencies must be amplified / boosted and where treble / high frequencies must be attenuated / cut in order to achieve the original sound that had been recorded. The corresponding pre-emphasis curve used for cutting the master disk is inverse.
When comparing with lists provided by the manufacturers of equalizer pre-amps it should be considered that those may be misleading, as they might not quote the correct parameters of the curve but rather the next-best possible settings of these devices. For example the Conductart OWL 1 Sound Restoration Module – a renowned pre-amp of the 1980s – offered settings of flat/ 250/ 375/ 500/ 750/ 1000/ RIAA for turnover and flat/ 5/ 8.5/ 12/ 14/ 16/ RIAA for roll-off. Thus for the widely used standard “AES 400N-12” settings of 375 Hz and -12 dB were listed; for the “Bartok 629C-16” curve it was 750 Hz and -16 dB and for “LONDON LP 500C-10.5” it was 500 Hz and -8.5 dB. These recommendations were quoted or copied by other authors and three “new characteristics” had come to existence.
Table 1 gives the three parameters to characterize any EQ curve: the turnover frequency f1 for bass shelf, f2 for bass boost and f3 for treble cut (or alternatively the three corresponding time constants τ1, τ2 and τ3). These are the necessary conditions to compute and plot any EQ curve, determine the correct settings of a digital equalizer or to solder an electronic filter circuit.
The gain at two typical frequencies will give you a rough impression of what the curve does to the audio from the record. The frequencies are:
  • 50 Hz, where usually the bass shelf becomes effective
  • 10 kHz, because the treble curve is often indicated by roll-off at 10,000 Hz
The very descriptive “code” is a good tool to avoid misunderstanding when EQ curves come under various alias names (what they do too often).
  • The first 3-digit number indicates the turnover frequency of bass boost (f2)
  • The letter in the middle is N … (“None”) if no bass shelving is applied, or R … 20 dB (named R after RCA or RIAA) B … 18 dB A … 16 dB C … 14 dB (named C after Columbia LP curve) X … 12 dB
  • The last number shows the reduction or roll-off of treble at 10 kHz and is always preceded by a minus sign. Please mind that this is only a code and that the exact value – after normalization to 0 dB at 1000 Hz – might be different.
This code can be used to find the correct settings of most equalizer pre-amps.
(Example: “RIAA 500R-13.7” means for the RIAA curve that bass must be boosted below 500 Hz, but no more than + 20 dB and that treble must be cut at 10,000 Hz to – 13.7 dB)
The geographic region and the time period are added to allow a qualified guess for the required EQ should a record label not be listed. In general, American recording curves were more deliberate in cutting bass and boosting treble. The British and Europeans tended to apply only the necessary minimum of bass attenuation and often no treble boost at all, that means they had a “flat” treble curve. Early pre-emphasis curves were simply built and rather soft. In the late years (after 1945) curves became highly sophisticated, with the third turnover frequency f1 added to manage the bass shelving and also with gain ranging from -20 dB to + 20dB.

Table 1: Playback Equalization Curves

Region
Timeperiod
Curve Name, alias names
Text
Time constants
Time constants
Turnover frequencies
Turnover frequencies
Turnover frequencies
Bass shelf
Bass boost
Treble cut
Text
τ1 [μs]
τ2 [μs]
τ3 [μs]
f1 [Hz]
f2 [Hz]
f3 [Hz]
[dB]
@ 50Hz [dB]
@10kHz [dB]
Normal Groove, 78 rpm
Eur., Brit.
1926 - 1946
"European 78", Old Europ.,250,EMI 78
636
250 [5]
+ 14,4
0 (flat)
250N-0
Eur., Brit.
1927 - 1946
"Blumlein 300"
531
300 [5]
+ 16
0 (flat)
300N-0
Brit., Amer.
1926 - 1950
"500-FLAT", Blumlein500, Europ.500
318
500
+ 19
0 (flat)
500N-0
America
1926 - 1951
"American 78"
636
250
5900*
+ 14
- 6
250N-6
America
1926 - 1951
"American 78"
636
250
4400*
+ 14
- 8
250N-8
Amer.(CBS)
1938 - 1948
"Columbia 78"
530
100
300
1592
+ 16,7
- 15,0
300N-16
Amer.(RCA)
1941 - 1947
"Old RCA" [4]
199
36,7
800
4340
+ 22,2
-9,9
800N-8
Eur., Brit.
1944 - 1956
"DECCA 78", FFRR 78, London ffrr 78
531
25
300 [5]
6366
+ 15,4
- 5,7
300N-5.5
Germany
1952 - 1955
"CCIR 78", Recomm. No.134 (1953) [1]
450
50
354
3183
+ 17,0
- 10,5
350N-10.5
Eur., Brit.
1955 - end
"IEC N78" = "B.S.1928" for N78 only
3180
450
50
50
354
3183
+ 16
+ 14,0
- 10,5
350A-10.5
Microgroove, 33⅓ and 45 rpm
America
1942 - 1949
NAB (broadcast transcriptions, 1942)
318
100
500
1592
+ 20,5
- 15,6
500N-16
America
6/1948 - 1956
"Columbia LP", Col. M33, "LP" [3]
1590
318
100
100
500
1592
+ 14,5
+ 13,6
- 15,5
500C-16
America
4/1949 - 1958
"NAB", NARTB (standard 1949) [3]
3180
318
100
50
500
1592
+ 20
+ 17,5
- 15,6
500"B"-16
America
1/1951 - 1958
"AES" (standard 1951)
398
63,7
400
2500
+ 18,1
- 12,3
400N-12.3
Amer.(RCA)
1947 - 8/1952
"RCA 45" (45 rpm) [6]
200
75
796
2122
+ 22,6
- 13.7
800N-13.7
Amer.(RCA)
1947 - 8/1952
"RCA Old Orthophonic" (33⅓ LPs) [6]
318
75
500
2122
+ 19,7
- 13.7
500N-13.7
Amer.(RCA)
8/1952 - pres.
"RCA New Orthophonic"
3180
318
75
50,05
500,5
2122
+ 19,5
+ 16,9
- 13,7
500R-13.7
Amer. (all)
ca.1956 - pres.
= "RIAA" (US-standard since 1955)
Europe
ca.1962 - pres.
= IEC No.98 (1955) = B.S.1928 (1955)
Amer., Brit.
1949 - 1956
"LONDON LP" [2]
1590
318
50
100
500
3183
+ 13,8
+ 12,5
- 10,9
500C-10.5
Germany
1955 - 1962(?)
TELDEC (as proposed 1957 for DIN)
3180
318
50
50
500
3183
+ 19,3
+ 16,5
- 10,9
500R-11
Citations
Table 1 is mostly based on Tab. 2a of: Heinz O. Graumann, Schallplatten-Schneidkennlinien und ihre Entzerrung, in: FUNKSCHAU 1958 / Heft 15, pp 359 ff* computed frequencies to get 6 or 8 dB @ 10 kHz
[1] CCIR used by Deutsche Grammophon modified with 50 Hz bass shelving => IEC N78 [Brice]
[2] Used by British Decca and for London releases in US and UK, mostly M33. Cf.: Wolfgang Leister, The London Curve, in ARSC Journal, vol.48:2, Fall 2017, p.163
[3] Gary A. Galo, The Columbia LP Equalization Curve, ARSC conference March 2008; Gary A. Galo, Disc Recording Equalization Demystified, in ARSC Journal Fall 1996
[4] Old RCA is one of the original RCA curves for shellacs. It continued to be used for 33⅓ LPs by RCA-Victor, Brunswick, Concert Hall, Coral, Decca (Amer.) and Westminster. The turnover f3 and the time constants are computed values for an equalizer set at 800N-8.
[5] 250 Hz or 300 Hz seem to be a question of personal listening preference, as explained in Individual fine tuning
[6] Robert C. Moyer, Evolution of a Recording Curve; in: Audio Engineering, vol.37, no.7, July 1953; pp 19-22, 53-54. Roll-off is frequently listed as between 10 and 12 dB, but this “flattening off” to ca 10 dB at 10 kHz was an intentional high cut which must not be compensated for in playback. Thus a setting of 13.7 dB is correct!

78 rpm EQ Curve Generator

EQ Curves for Audacity can be generated from these Frequency and Roll-off values using the experimental Nyquist plugin "78 RPM EQ Curve Generator". This plugin is obtainable from the top of this Forum topic and requires Audacity 1.3.13 or later. Please give feedback on this plug-in, or ask for help if you need it, by replying to that Forum topic.
  1. 1.
    Extract 78EQCurveGen.ny from the zip file downloaded from the above Forum topic.
  2. 2.
    Place 78EQCurveGen.ny in the "Plug-Ins" folder inside the Audacity installation folder, then launch or restart Audacity. For more help installing the .ny file to the correct location, click here.
  3. 3.
    Click . You can find help inside the plugin by choosing one of the Help options in "Select Function or Help".
  4. 4.
    Choose the curve you want from one of the lists.
  5. 5.
    Enter the values for your chosen curve for
    • "Bass Turnover Frequency (Hz)"
    • "10 kHz Gain Roll-off (dB)"
    • "LF Shelving Frequency (Hz)" (if a value is given)
    in the equivalent boxes in the plugin dialog.
  6. 6.
    Click "OK" in the plugin to save the .xml file to your chosen location.
  7. 7.
    Use the EQ XML to TXT Converter Tool to convert your XML file to a TXT text file (suitable for Audacity 2.4.0 and later)
  8. 8.
    Select some audio and choose .
  9. 9.
    Choose "Manage".
  10. 10.
    Choose "Import...", navigate to the location where you saved the .txt file.
  11. 11.
    Click "Open".

EQ Curves Library

Here you can find some useful EQ curves for download to Audacity for use in Effect -> EQ and Filters -> Graphic EQ and Filter Curve EQ. (Curves are in TXT file format, as required in current Audacity and compatible down to version 2.4.0).

78 rpm shellacs

EQ Curve file
Description
500-FLAT_3.2.2.txt
500-FLAT 500N-0 was used by British Columbia, EMI, His Master’s Voice, MGM and Parlophone between 1931 and 1953. Later releases have modified treble.
American_78_3.2.2.txt
‎American 78 – 250N-6/250N-8: Common setting for many American shellacs. This curve here is a compromise between both varieties with -7 dB roll-off.
BBC_Transcription_(1949)_3.2.2.txt
BBC 2dB/octave: used by smaller British labels (Aco, Broadcast, Linguaphone, Vocalion, …) from 1926 to 1933, which had their recordings mastered by BBC with the Marconi system.
Blumlein300_3.2.2.txt
Blumlein300 - 300N-0: A British traditional for Gramophone Company, Decca, Columbia and EMI (1930s – 1944).
Columbia_78_3.2.2.txt
‎Columbia 78 – 300N-16 is the right one for American CBS-Columbia shellacs (1938 - 1948).
Decca_78_3.2.2.txt
Decca 78 – 300N-5.5: For Decca and London shellacs featuring the ffrr (full frequency range recording) system. Here in the version of Copeland/The British Library Sound Archive
European_78_3.2.2.txt
European 78 - 250N-0 is a common setting for European shellacs (1926 – ca. 1944), especially for Columbia and His Master’s Voice produced by EMI (UK), Cetra and Cetra-Soria.
European_78_3.2.2.txt
Telefunken 400N-0: used by European Ultraphon, Supraphon and Turicaphon from 1929. Also used by Telefunken – after the takeover of Ultraphon – until mid 1950s.
Western_Electric_3.2.2.txt
Western Electric: Very early Columbia and Victor recordings (1926) used a bass turnover frequency of 250 or 300 Hz but their treble is described as “flat”. The perceived treble amplification was possibly only the result of resonant peaks of the early Western Electric condenser microphones used in recording. The above download is an experimental replay EQ curve for this microphone / pre-emphasis combination. Additional background information is given in this PDF.

pre-RIAA 33⅓ LPs

EQ curve files
Description
AES_(1951)_3.2.2.txt
‎AES – 400N-12.3: Intended by AES (Audio Engineering Society) as a replay standard for many American shellacs of the 1930s and 1940s. Also used by many record producers as a recording curve for N78 and M33 between 1951 and 1958. Also to replay Capitol and Capitol-Cetra recordings with “Capitol curve” 400N-12.7 (1951 – 1955).
Columbia_LP_3.2.2.txt
Columbia LP – 500C-16: For Columbia and many other labels, mostly 33⅓ LPs (M33).
London_LP_3.2.2.txt
London LP – 500C-10.5: Used for British Decca and for London / Decca releases in the US featuring the ffrr (full frequency range recording) system. Mostly 33⅓ LPs (1949 – 1956)
NAB_(1949)_3.2.2.txt
NAB – 500B-16: A widely adopted standard of NAB / NARTB (National Association of Radio and Television Broadcasters) requiring ca. 6 dB more bass boost than Columbia LP
RCA_45_3.2.2.txt
RCA 45 – 800N-13.7: RCA’s curve for their 45 rpm discs (1949 – August 1952). Possibly identical with Technichord’s “Technichord curve” 800N-12 already used since 1938 for their 78s.
RIAA.txt
RIAA = RCA New Orthophonic – 500R-13.7
RCA_Old_Orthophonic_3.2.2.txt
RCA Old Orthophonic – 500N-13.7: RCA’s curve for 33⅓ LPs (1950 – August 1952) and for LPs mastered by RCA for other labels. Possibly identical with “MGM curve” 500N-12 used by MGM.

Individual fine tuning

In some cases it will be not enough to apply the correct EQ to get the desired result. According to the condition of the record and to personal listening preferences you might consider one of the following methods:
  • The 250-or-300-Hz dilemma: To use “European250” or “Blumlein300” EQ seems to be not a question of right or wrong but of personal listening preferences. In general, Continental European authors prefer 250 Hz (derived from the original Western Electric recommendation) for Decca (Brit. and Europ.), Brunswick, Cetra, Columbia (Brit.), EMI-HMV and Parlophone. Englishman Copeland favors 300 Hz (derived from the recording characteristic of the Blumlein cutter) for British EMI, His Master’s Voice and Columbia and also for Odeon. Copeland puts it like this: “[…] but when I’m not sure I use 300 Hz.” [Copeland, Manual, p 129]. Being derived from the previous 250-or-300-Hz curve the same applies to “DECCA78” which was used from 1944 for shellacs with the ffrr system. So you should also feel free to decide the 250-or-300-Hz question according to your own listening preference: 300 Hz will give an extra amplification of bass in play back (ca 1.5 dB at 50 Hz).
  • To remove low frequency noise Robinson (MidiMagic) recommends a low cut filter at 100 Hz with just 6 dB/octave. (Especially for many acoustic recordings which have only noise below 150 Hz or for the “long-playing” shellacs of RCA Victor of 1931/32). This filter will do exactly the same as the “C”-type bass shelf of Columbia LP curve.
  • Vadlyd uses a variable low cut filter for American Victor, early British Decca, EMI, His Master’s Voice and Columbia at frequencies between 40 and 70 Hz. This is very similar to the recommendation of Phonomuseum.org. In Audacity you can experiment with different settings for “Frequency” and “Roll-off” in Effect -> High Pass Filter (a different word for Low Cut Filter) and listen to the result with “Preview”.
  • All bass shelf settings on analog equalizers (R-B-A-C-X) can also be used to remove low frequency noise (especially from acoustics and early shellacs). This is why the extra positions X and A were provided [MidiMagic]
  • A known trick of recording engineers was to increase bass t/o frequency on very long recordings. Thus bass attenuation was increased and bass amplitude and necessary groove width were reduced. So the given duration of the audio could be squeezed into the given space on the disc. If a disc is filled with grooves as can be a higher bass turnover frequency can be necessary to restore the original sound. Example: Colosseum [ES]
  • To improve the weak bass on some 45s (especially on EPs – Extended Play) Esoteric Sound uses a higher turnover frequency for bass in replay than in pre-equalization. For example 700 Hz instead of the “correct” 500 Hz. This will give a smooth, extra bass amplification of roughly 4 dB at 50 Hz.
  • To reduce surface noise of early American Columbia, Victor and RCA-Victor iasa recommends an additional high cut (= low pass) filter set to 5500 or 5200 Hz with 6 dB/octave. This will reduce treble by 3 dB at around 5000 Hz and by 9 dB at 10000 Hz – and hopefully most of the noise.

Remarks for Analog Purists

  • Hiss and high frequency scratch due to old worn records: When digitizing such recordings Audacity’s will do a good job to improve the sound once and for all. Those who prefer entirely analog replay with an adjustable pre-amplifier will have the opportunity to improve the sound every time they replay. They can cut / attenuate the frequency range most affected by the noise. A higher value for roll-off at 10 kHz than the “correct” EQ will usually give a better result than a simple treble filter – but: at the expense of the high frequencies of the audio itself.
  • Dull, lifeless sound: If you improve poor bass on discs of any speed by choosing a higher bass turnover frequency than the “correct” EQ, there will be the welcome side effect of moderately amplifying midrange frequencies. This will bring life to the core octaves of a piece of music by improving instrument and vocal characteristics.

Acoustic recordings and Broadcast Transcription Discs

Acoustic recordings (before 1926) are beyond the scope of this page. In these pioneer years speeds varied from 70 to 90 rpm, groove modulation could be lateral, vertical or diagonal and some records were even cut outward with the audio starting at the center. A special turntable and a range of styli / needles are needed to replay.
All acoustics were recorded without any pre-equalization, simply because a modification of the audio was impossible before electric microphones and amplifiers came into use. Nonetheless there are conflicting opinions as to the result:
According to various authors the acoustical recording process had an "inherent mechanical equalization", which results – within the limited frequency range of approx. 150 to 4000 Hz – in a constant velocity characteristic one would only expect from a magnetic cutter. With a magnetic cartridge this would command to be replayed “flat”. Please note that the acoustical recording characteristic is not equalized at all.
According to Robinson an acoustical recording must have a constant-amplitude characteristic which will be correctly reproduced by playing back with a gramophone needle or a piezoelectric crystal pickup. A magnetic cartridge will – by its constant velocity characteristic – double the amplitude whenever the frequency doubles. To compensate for the magnetic pickup MidiMagic recommends an “800N-16” EQ curve, which comes close to the theoretical characteristic of a constant velocity device. Some more information is here on record labels and on technical background. Please note that the acoustical recording characteristic is not equalized at all.
Kolkowski’s results of a reenactment of an acoustic recording session show that bass needs heavy equalization if the losses in the recording horn (here below 400 Hz) shall be compensated for. Parametric equalization may be used at resonant frequencies. Treble should be amplified (!) to compensate for the high-frequency roll-off of the recorder. Due to the individual properties (defects) of recording horns and recorders there will be no “general characteristic” of acoustics and therefore no general EQ.
MidiMagic gives useful information on vintage labels as Edison, Berliner, Pathé or Zonophone and playback EQ recommendations.
Scientific help regarding valuable historic recordings can be found at IASA (International Association of Sound and Audiovisual Archives) and at ARSC (Association for Recorded Sound Collections).
Broadcast Transcription Discs are not in the focus of this page either. Those were recordable lacquer discs, mostly 16 inch in diameter, played at 33⅓ or 78 rpm. They were professionally used by radio broadcasters. Some more information is in this PDF.
In America many of these discs were recorded under the standard of the National Association of Broadcasters (NAB) of 1942. The very same recording curve had been used by NBC under the name “Orthacoustic” since mid 1930s. This “NAB Transcription (1942)” playback EQ setting can be downloaded here.
The British Broadcasting Corporation (BBC) used a rather exotic curve as a house standard. The version in use after 1949 has been reconstructed from Longford-Smith’s publication of 1952 as an Audacity EQ setting “BBC Transcription (1949)” and can be downloaded here.

78 rpm shellac labels and their EQ

This page is about electrical recordings since 1925 on 78 rpm discs made of shellac! The invention of the Electrical Recording System by Bell Laboratories / Western Electric which was licensed to industry leaders Columbia Records and Victor set some de-facto standards: speed is always 78 rpm, cut is always lateral (same as later mono LPs) and the groove type is always Normal Groove (also named coarse groove). Therefore shellacs are sometimes referred to as N78 (which stands for normal groove discs, played at 78 rpm).
A turntable capable of 78 rpm will be useful. You will need a MONO stylus with 2.5 mil (64 μm), for early electricals possibly one with 3 mil (76 μm) and this Audacity Wiki!
It is assumed that you replay your discs “flat” (without any analog de-equalization) and apply the necessary EQ after digitizing with Audacity . If it is necessary to play the record through a system that applies modern RIAA equalization, select the "RIAA" curve in Audacity's Filter Curve EQ effect and use the Invert button to invert and thus remove the incorrect RIAA equalization before applying the appropriate equalization to the recording.
In case sources did not agree on one EQ curve, their different opinions are listed and you will have to trust your ears.

Table 2: 78 rpm Shellac Labels and Their EQ

Label
Remarks
Curve Name
Code
turnover bass [Hz]
bass shelf
treble roll-off [dB @ 10kHz]
Source
_Electrical 78's (general)
1925-1938
300
0
ES
_Electrical 78's (general)
1932-1938, mid 30s
500-FLAT
500N-0
500
0
ia,ES,JP,RF
_Electrical 78's (general)
1938-1946
300 or 500
0 or -5
ES
_Electrical 78's (general)
1947-1954
300 or 500
-16
ES
Aco
1926 - 1933, British, with M in a circle
BBC 2dB/oct.
PC
Aeolian-Vocalion
1926 - 1933, British, with M in a circle
BBC 2dB/oct.
PC
ARC
American Record Corporation = Cameo + Pathé + Plaza Group; 1929 - 1930
500
0 or -5
PC,JP
ARC
American Record Corporation; 1930 - 1939 (some early also 500-5)
500
-8.5
JP
Argo
American 78
250N-6
250
-6
mm
Ariel
1925 - 1931, British, with Δ after matrix no. or with W in a circle
[W.E.]
250
W.E.mike
PC
Artist
500
-16
ES
Audiophile
1952 - 1955, 78 rpm microgroove (!) records, up to AP-30; may also be replayed with "flat" treble
Audiophile78
300N-8
300
-8
RH,Mc,AT
Autograph
Marsh Laboratories, ca. 1924 - 1926
1000
0
ES,JP
Banner
1926 - 1929, an ARC label from 1929
500
0
JP
Balkan
500
-5
ES
Beltona
1926 - 1933, from cat. 1194 to 1282, with M in a circle
BBC 2dB/oct.
PC
Beltona
1944 - 1955, ffrr, prod. by Decca UK,
Decca 78
300N-5.5
300
-5,7
PC
Bluebird
sublabel of RCA, see: RCA-Victor
Bluebird
1925 - 1931, with VE in an oval or "Orthophonic Recording" or with Δ after matrix no. (recorded in Europe)
[W.E.]
250
W.E.mike
PC
Broadcast (American)
American 78
250N-6
250
-6
mm
Broadcast (American)
1940s
500
-12
JP
Broadcast (British)
1926 - 1933, with M in a circle
BBC 2dB/oct.
PC
Brunswick (American)
1925 - 1930
500-FLAT
500N-0
500
0
ia,JP,RF,PC
Brunswick (American)
1929 - 1935, an ARC label from Dec 1931 to 1940
500
-5
JP
Brunswick (American)
1935 - 1939
500
-8.5
JP
Brunswick (American)
1946 - 1951 or 1954, a Decca (Amer.) label since 1941
630N-?
629
-8 or -12
ES,mm
Brunswick (British)
1925 - 1944, a Decca label since 1932; see: Decca (Brit.)
European 78
250N-0
250
0
ES,GH
Cameo
1926 - 1929, probably W.E.; an ARC label from 1929
[W.E.]
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