Digitizing 45RPM ... Speed? - AVS Forum
View Poll Results: Should a 45 RPM recording be first digitized at 33+1/3 RPM and the recording upscaled in order to ma
Yeah, higher frequencies = more data = clearer sound 0 0%
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Old 06-28-2013, 10:01 PM - Thread Starter
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Hello all,


I've been thinking about getting some high-resolution FLAC files off some of these old 45s I picked up over at the pawn shop for a few bucks. They're not in the best condition, but they make pleasant sounds, and that's awwwright.

Anyways, this fancy USB turntable allows for recording in up to 48khz/16bit audio and has three speeds with quartz speed lock - 33, 45, & 78. I was disappointed that the turntable only would let computer have 16bits, and especially disappointed in 48khz, so I came up with an idea ...

Perhaps I could record this 45 at 33+1/3 ... Then I could double the sample rate and halve the speed in Audacity, creating a 96khz version of the 48khz track. This perfectly preserves the 48khz track, but effectively doubles every piece of data. I could then use speed correction to up the speed 35%, giving some higher frequencies than 24khz (and a generally higher quality overall).

Or so I thought ... My concern is that the digitized material recorded at a lower speed will amplify any surface noise present (which is everywhere on these dusty suckers). Also, won't bass frequencies suffer? Is this small amount of bass loss a worthy cost for the incredibly amount of treble gain (which has now shot from from 24khz close to 30khz according to Audacity's useful spectogram)? Another issue is all that unused data in the 96khz track ... why have 96 khz when only 60 are used? Is this file space a big enough deal?

Well, I'm really unsure about all these questions. So I thought I might ask some pros.

Attached I've included two small snipets.
1) 20 seconds or so of an album recorded at 33+1/3 rpm, digitally doubled to 96khz, and sped up to 45 rpm.
96khz.zip 3725k .zip file

2) The same 20 seconds or so of the same album, but recorded at 45 rpm (still 48khz).
48khz.zip 2332k .zip file


I've tried using Foobar to ABX the two tracks, but still can't decide ... All opinions are appreciated!


Thanks,
Ezra
Attached Files
File Type: zip 48khz.zip (2.28 MB, 4 views)
File Type: zip 96khz.zip (3.64 MB, 7 views)
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Old 06-28-2013, 10:19 PM
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Hi Ezra,

In theory, you may be able to squeeze some resolution improvement, but I'm not sure it is worth it. A decent sound-card or USB audio interface from the analog outputs would go much further.

But my main concern is that, by slowing the record down, you are obviously decreasing the frequency of the music proportional to the speed difference. So the phono-preamp is no longer applying the RIAA curve where it should be.
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Old 06-28-2013, 10:29 PM - Thread Starter
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I'm assuming the analog signal is converted to digital in the turntable - All I have to do is supply the same type of cord I use to hook up my printer. But is this the fault of a turntable's crappy ADC or, as you said, the sound card? As far as sound cards go, I'm on a newer laptop, but I don't think even newer models support upgrades to that region very well ....

But hey, I never thought of that EQ plobrem. ... Well I suppose once the 33+1/3 is done recording in Audacity, I could invert the RIAA curve, apply that, speed 'er up, then re-apply the correct curve.
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Old 06-29-2013, 07:13 AM
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You got some old records that are not in perfect condition and you are worrying about those miniscule differences?

That is absolutely ridiculous,

Just play the damn records at 45 RPM and use any good CD-quality 16-bit conversion and you will have a very good result.
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Old 07-01-2013, 02:42 PM
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Hi Ezra,
Quote:
Originally Posted by Ezra Lesser View Post

I'm assuming the analog signal is converted to digital in the turntable - All I have to do is supply the same type of cord I use to hook up my printer. But is this the fault of a turntable's crappy ADC or, as you said, the sound card?
Sorry, I wasn't very clear, and probably caused some confusion.

Indeed, the A-to-D conversion is taking place within the turntable if you are using the USB interface. In that situation, any sound-card within your computer is not being used.

However, I made an assumption that the turntable also had a pair of analog-audio outputs. If it is a cheap turntable, then it may not. My suggestion was to bypass the USB interface altogether and use a higher quality sound card in combination with the analog outputs if you weren't satisfied with the result from the USB.

As Commsysman said, you may be trying to squeeze blood from a stone. Although I would agree with him to some extent, I also know that the digital versions of vinyl recordings can be improved with the right combination of post processing. When it comes to removing scratches, pops and clicks, a higher resolution file can be useful, but only if there is higher resolution content to process, which your cartridge might preclude.
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