Recording 33 1/3 LPs at 78 RPM

As the subject says I am wondering what would be the impact of recording 33 1/3 RPM lps at the faster 78 RPM then using Audacity’s “Change Speed” feature to slow the audio back down. Here is the thing, I have several LPs to convert and thought that I could shorten the task by recording them at high speed. However I have no idea what impact this may have on the resulting audio files. Will I lose any audio information in the speed change process?

I understand that 78’s used a different size needle but that should not be an issue as I will be recording with a standard “micro-groove” needle just at the higher turntable speed. I also understand the the equalization for the two speeds are different…not sure what if any impact this may have.

Can anyone shed some light on this for me?


I’m no expert on this - but my understanding from reading earlier threads is that you will lose high frequency signa.Personally I wouldn’t (and didn’t) do it this way. I enjoyed listening to the records as they all got transcribed (And I did upwards of 250 plus my 45s and still have yet to tackle my wife’s collection also c. 250 plus LPs and many singles)

The bigger needle that is used for 78 records is used because the grooves themselves are wider. You will be recording microgroove vinyl with a styus size that is designed for it so you will be ok

The differeent RIAA equalizations are for the different types of the recording shellac 78s versus vinyl LPs &45s- the playback speed iself has no bearing on this. You will need to pass the signal through a phono preamp (or your TT may have a built in preamp) to get the RIAA equalization applied in hardware (normally bettter that doing it post-capture in software with Audacity)


Thanks for your reply…a followup question

I am assuming that my turn table (a Memorex 2650MMO) has a built in pre-amp when using the USB output. Does this mean that the equalization will be applied automaticaly (by the TT) based on the selected speed?


Yes, USB TTs (normally) have an in-built preamp to pass the analog signal through prior to passing it in to the on-board ADC (Analog to digital Converter) and thence on the the USB services for output.

As I explained earlier the RIAA applies is a function of the record type being played rather that the speed of playback. It is possible that the T you have has cunning enough circuitry to apply different RIAA curves when playing at different speeds - but for the price of the device I somehow doubt it.


Sorry for being a bit dense here but what do you mean that the RIAA is a function of the record type?

I had always thought that the RIAA curve (based on the record type/speed) was applied to the LP master at recording time and then had to be matched at playback time. To me this would imply that either the TT, the pre-amp or some other piece of equipment would have to apply the correct RIAA curve for the type of album being played. I think this equalization would most easily be applied by the pre-amp and it seems a small thing (if the pre-amp is built into the TT) for the appropriate curve to be applied based on the speed selected on the TT.


Yes correct.

Shellac 78’s had a different RIAA curve applied by the engineers when mastering - different fro the one used for vinyl. In fact not jus a different one but rather many different ones. Prior to viny there was no standardixation of the RIAA equlaization curve and each manufacturr used their own version - some manufactures even used mor than one version (if you look in the Audacity Effect>Equalization dropdowns you will see several different equalization curves for 78s - and the list is by no means exhaustive).

My comment about proper 78 equlaization being applied by your TT is based on the above fact of the many different 78 RIAA curves - so it’s extremely unlikely that the naufacturer of your TT would go to all the trouble to build in all the “correct” 78 Eq curves.

BTW: folks who record 78s often need to reverse the vinyl RIAA and then apply the correct 78 version - there has been a recent feature request thread about just this on the forum).

But you need be concerned by this - you are recording vinyl (at whatever speed you choose) and it is likely therefore that the correct RIAA curve will be applied for you. Even if you do go on to record your LPs at 78rpm ypu will still need the vinyl RIAA Eq …


Ah, I get it now thanks for the explanation.

Could you elaborate on the loss of fidelity when recording this way (high speed). Is it caused by the high speed recording or by the later software speed reduction?

Thanks again for all the help/info.

Aahh …that’s the bit that’s beyond my “pay-grade” in terms of technical expertise. So I don’t intend to make a fool of myself by blathering on about it :slight_smile:

Hopefully one of the professional sound engineers who inhabit this forum can chip in with a bit of an explanation.


Consider the case where you have a superbly-recorded 33 1/3 rpm vinyl LP that contains audio with frequencies ranging from 20 Hz to 20,000 Hz (the nominal full range of human hearing). When you play it back at 78 it will sound like chipmunks on helium, right? In effect you have translated that original frequency range to the range of approximately 47 Hz to 46,800 Hz. Now the cartridge that is playing back these frequencies was designed to reproduce the 20-20,000 range, and if it’s really, really high end it might be able to reproduce frequencies up to 25,000 Hz. So everything from 25,000 Hz upwards is lost during high-speed playback. You end up with recorded frequencies in the range 47 Hz to 25,000 Hz. Now we use software to reduce the speed back to normal. The chipmunks become human again. And the resulting frequency range we’re left with is 20 Hz to 10,700 Hz. See what happened? You lost all the high frequencies. This is assuming the best possible recording with the best possible cartridge and no losses during the software speed-reduction step. The results will be even worse if the cartridge is average - if it cannot reproduce frequencies above 20,000 Hz your resulting recording (after speed reduction) will have no frequencies above 8,500 Hz - we’re getting into AM radio sound here.

Now this is just the first part. The second part involves the RIAA playback equalization (EQ). The LP was recorded with this EQ curve at normal speed. When you play it back at high speed all the frequencies are shifted and the playback EQ curve is applied to the wrong frequencies. This would also need to be corrected in software.

Third, even if your cartridge could reproduce frequencies up to 50,000 Hz (which is highly doubtful), there is no guarantee that your pre-amp will pass these frequencies, and even if it did it is highly unlikely that the playback EQ curve would be well-defined at frequencies above 20,000 Hz.

Not only will your recordings sound muffled, you will damage your LPs by doing this. The stylus that tracks the groove in the record is part of a mechanical system. When it can’t move fast enough to follow the grooves (which is what happens when you play a 33 at 78), it just ploughs through the grooves, inflicting permanent damage.

Have I convinced you? Don’t do it. It is not worth the hassle even if it did work, but it almost certainly won’t work, and will damage your LPs.

– Bill

<<<Shellac 78’s had a different RIAA curve >>>

Worse, it wasn’t an RIAA curve. The Recording Industry Association of America (back when they were the good guys) standardized the equalization in phonograph records in 1952. Sound will not fit on a phonograph record and must be distorted. Before 1952, everybody had their own distortion that was Much Better than everybody else’s. RIAA took care of that. Here’s the standard, have a happy day.

And they did.

Running a record fast to “get it over with” has one problem above all else. The needle is designed to vibrate and move very accurately only in a narrow range. Exceed that range and the needle stops picking up the music. What’s the speed limit on your street? I think mine is 35 MPH. What chances do you think me in my pickup truck (lorry) would have on the same street at 95? You think I would make all the turns, or do you think I might miss a few?

I don’t think I’d make it past Mrs. Chen’s Mexican Fan Palm at the end of the block.


Bill, thank you for that very clear answer…and yes you did talk me out of it.

Despite the fact that I have been “talked out of it”, I am still a bit confused by the RIAA EQ thing. I understand that the curve applied during mastering was based on the normal playback speed what I do not understand is why that would not be “made right” again by the speed changing software. Since the EQ is built into the recorded audio would it not still be there, correctly, when the audio data was slowed back down?

As I said you did completely talk me out of doing this I am just curious on this point.


The equalizer inside the turntable assumes each tone coming from the record needs its own special, specific processing. If you play the record at the wrong speed, all the tones are in the wrong place.

You’re going to ask, why don’t I play the record without the equalization and do the whole thing in post production. Yes, that’s the only way this would come even close to working.

Unfortunately, the connection from the needle is very special, too, and you can’t just jam the cartridge wires into your computer or music amplifier.


Is this EQ done by the TT or by the pre-amp? This is exactly what I was asking a previous poster. He made the point (and it makes sense to me) that in my cheap-o TT (a Memorex 2650MMO) with it’s USB output, EQing was probably not included.

Nope, I was not going to ask that one…I truely have been talked out of this by Bills excellent explanation of the problems with doing it.

Every USB turntable includes RIAA playback EQ. This playback EQ is actually done in the phono pre-amp stage. A USB turntable must include a phono pre-amp to a) apply the proper playback EQ, and b) boost the tiny signal from the cartridge so that the analog-to-digital converters have a large enough signal to work with.

This is a tough one to get your head around, I admit. The playback EQ is applied before the sound gets into Audacity. When you slow down the recording in Audacity you also shift the EQ down by the same amount. So the EQ is effectively applied to the wrong frequencies. Put another way, it’s like you applied a different EQ curve on playback.

One way to get the EQ right is like this.

  1. Play back at double speed (or whatever) and record into Audacity. RIAA playback EQ is applied and there’s nothing you can do about it.
  2. In Audacity, reverse the RIAA EQ. Now you have a “flat” un-equalized copy of the record.
  3. Adjust the speed to normal.
  4. Apply the normal RIAA playback EQ.

– Bill

Ah, well that makes sense then.

Ok, I think I get it.

All this has been assuming you’re going to get a crisp, clear, clean, perfect playback on your USB turntable.

No, probably not. One of the other elves got one and was so disappointed with the playback he put it in the garage and dug out his old conventional turntable and brought it back to top operation to do his transfers. My semi-pro turntable has never been out of operation.


Actually … he managed to sell it to one of his friends who is less fussy about audio quality and places a higher value on convenience/ease-of-use. :blush: