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Topic: CD album slowed down to 33 1/3 rpm (Read 2109 times) previous topic - next topic
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CD album slowed down to 33 1/3 rpm

I want to slow down a ripped CD album's wave files to effectively sound as if it were played on turntables at 33 1/3 rpm.

That is, a 45 rpm record played at 33 1/3 rpm.

How do I do this effectively?

In Audacity, is it simply a case of changing the tempo by -25.926% ?

Effect > Change Tempo > Percentage Change: -25.926%

btw Audacity labels this effect screen as: Change Tempo without Changing Pitch.

I have done with one track and it sounds ok, but I can't compare to how it would sound if I had the vinyl and record player set to 33 1/3 rpm.

It did try the Change Speed effect and it lost half of the frequency and sounded terrible.
 

Re: CD album slowed down to 33 1/3 rpm

Reply #1 –
Change speed is what you need, not Change tempo.
Quote from: jaybeee on
It did try the Change Speed effect and it lost half of the frequency and sounded terrible.
This is how it should be.

Re: CD album slowed down to 33 1/3 rpm

Reply #2 –
just 2 things needed:
1) resample to a higher sample rate (proportionally)
2) change the sampling rate back to 44100 without resampling (edit the file header, or do something that's equivalent of it, doesn't matter)

2) can be done with https://ffmpeg.org/ffmpeg-filters.html#asetrate (make sure to also use same PCM output format to avoid any loss) 
1) can be done with ffmpeg too, leaving it all in 1 command, but by default ffmpeg resampler works with low quality, need to add options to force it to use something better
https://ffmpeg.org/ffmpeg-resampler.html#Resampler-Options
a fan of AutoEq + Meier Crossfeed

Re: CD album slowed down to 33 1/3 rpm

Reply #3 –
the sampling rate is thus
44100 Hz * (45 / (33 + 1/3)) = 59535 Hz

and the command could be this (assuming that your file is 44100Hz and that there's no need to correct for any clipping which could appear after resampling)

ffmpeg -i "input file.wav" -c:a pcm_s24le -af aresample=59535:resampler=soxr:precision=28,asetrate=44100 "output file.wav"

resampling should be done to the album as a whole, by the way, otherwise it won't be gapless.
a fan of AutoEq + Meier Crossfeed

Re: CD album slowed down to 33 1/3 rpm

Reply #4 –
Quote from: Rollin on
Change speed is what you need, not Change tempo.
Quote from: jaybeee on
It did try the Change Speed effect and it lost half of the frequency and sounded terrible.
This is how it should be.
Ok, thanks. I feared that might be the answer.
Why is the frequency range affected so much? My knowledge lacks in this area of audio manipulation, so I'm guessing it's "simply" due to the processing made to the audio.

Quote from: magicgoose on
the sampling rate is thus
44100 Hz * (45 / (33 + 1/3)) = 59535 Hz

and the command could be this (assuming that your file is 44100Hz and that there's no need to correct for any clipping which could appear after resampling)

ffmpeg -i "input file.wav" -c:a pcm_s24le -af aresample=59535:resampler=soxr:precision=28,asetrate=44100 "output file.wav"

resampling should be done to the album as a whole, by the way, otherwise it won't be gapless.
Thanks for the explanation and code.

I tried it and it worked. It does however give the same sound/sonic output when using the inbuilt Audacity Change Speed Effect > Standard Vinyl rpm: 45 to 33 1/3

Although your method with ffmpeg results in: 24 bits | 2117 kbps | 145mb (original file 70.5mb)
Audacity's Change Speed Effect method results in: 16 bits | 1411 kbps | 95.2mb

Both change the original file from a duration of 6:59 to 9:26 - so at least your working out was correct :-)

--

Maybe - probably! - a stupid question: would the same audio output occur (frequency range being negatively affected) if the vinyl was played at 33 1/3 rpm and recorded to a digital format? I assume so.

Re: CD album slowed down to 33 1/3 rpm

Reply #5 –
Quote
Maybe - probably! - a stupid question: would the same audio output occur (frequency range being negatively affected) if the vinyl was played at 33 1/3 rpm and recorded to a digital format? I assume so.
I guess you are too young to remember records.  ;)
Yes.  Speed and pitch go down together.    The same thing happens if you play an analog tape at the wrong speed.   Frequency is the speed/rate of the wave.   A woofer moving back-and-forth at 20 Hz (20 cycles per second) is moving more slowly than a tweeter moving back-and-forth at 20kHz.   

When you slow-down a record the stylus follows the grooves more slowly.

If something gets fouled-up digitally and you end-up playing a 44.1kHz file at 22,050Hz it will play back at half speed and half pitch.


With "fancy digital processing" you can change tempo and pitch independently.

Re: CD album slowed down to 33 1/3 rpm

Reply #6 –
Quote from: DVDdoug on
Quote
Maybe - probably! - a stupid question: would the same audio output occur (frequency range being negatively affected) if the vinyl was played at 33 1/3 rpm and recorded to a digital format? I assume so.
I guess you are too young to remember records.  ;)
aye, a young whipper snapper of 42 lol.  I do own some vinyl, but never owned a turntable. My parents did, but I swiftly got told off for trying to scratch some records as it'll feck the stylus oops.


Quote from: DVDdoug on
Yes.  Speed and pitch go down together.    The same thing happens if you play an analog tape at the wrong speed.   Frequency is the speed/rate of the wave.   A woofer moving back-and-forth at 20 Hz (20 cycles per second) is moving more slowly than a tweeter moving back-and-forth at 20kHz.   

When you slow-down a record the stylus follows the grooves more slowly.

If something gets fouled-up digitally and you end-up playing a 44.1kHz file at 22,050Hz it will play back at half speed and half pitch.


With "fancy digital processing" you can change tempo and pitch independently.
Thanks