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Topic: Spectrals Question (Read 4282 times) previous topic - next topic
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Spectrals Question

Hi, I'm fairly new to this so sorry if this is a dumb question or poorly phrased.

I recently got some vinyl records digitized by a guy who has the required setup (I don't at the moment).  I don't know his exact signal chain, other than he's a DJ who uses a Technics SL-1210 and a Stanton 500AL stylus, who says he recorded them to wav at 16/44.  I looked at the spectrals in audacity and they all sort of look like this, with very little above 16-17 khz.

Song 1 full:
http://i.imgur.com/pEZZ1M6.jpg

Song 1 zoomed:
http://i.imgur.com/UyigM2o.jpg

Song 2 full:
http://i.imgur.com/9gXH8sF.jpg

Song 2 zoomed:
http://i.imgur.com/un5Ssau.jpg

What I'm wondering is what this information means.  I looked up the 500AL stylus and it's specs listed a frequency range of 20hz-17khz.  Is that what's responsible for the look of these, or could it have been something else in the signal chain?  I know that kind of roll-off is sometimes associated with mp3s, but these don't look the same as mp3s in my collection, and I'm pretty sure this guy is on the level.

Spectrals Question

Reply #1 –
Some kind of lossy compression, maybe MP3.

Spectrals Question

Reply #2 –
Looks lowpass filtered.  Could just be his recording software.

Spectrals Question

Reply #3 –
Most vinyl comes from a digital source. After all, recording, mixing and mastering is generally done in the digital domain since the 1980's. Even many instruments are digital nowadays. It's therefore possible that someone used MP3 to create vinyl records.

However, if this vinyl was pressed from an MP3 source I would have expected more signal above the cut-off. Playing vinyl can produce all sorts of pops, cracks, ticks etc. that I'd expect to show up all across the spectrum.

That's why I also suspect there is some lowpass filter in your friend's recording chain.
Every night with my star friends / We eat caviar and drink champagne
Sniffing in the VIP area / We talk about Frank Sinatra
Do you know Frank Sinatra? / He's dead

Spectrals Question

Reply #4 –
I agree with lvqcl that it looks like lossy compression rather than lowpass. Look at the OP's zoomed pictures carefully there are many "holes" in the spectrum begin at about 13khz.

I've included screenshots of lowpass at 16khz vs lame v4 to show the differences.
http://www.hydrogenaud.io/forums/index.php?showtopic=110044

Just my guess: "Oh shit! I saved in a wrong format and deleted the sources already  but wait, no one will know about this, to save my time just convert them to wav again

Spectrals Question

Reply #5 –
Is there any of these popcracklehiss-removal applications that could produce such artifacts? (Or even a vinyl-to-digital suite that outputs to mp3 in a default setting, and the user is ignorant enough to decode to .wav?)

Spectrals Question

Reply #6 –
Quote from: Porcus on
Is there any of these popcracklehiss-removal applications that could produce such artifacts?

Noise reduction process can create holes in spectrum but it will not make a sharp cut above certain frequencies. It is usually done by selecting a portion of the source file which only contain noise (such as start or end of a track) as a "noise profile" then remove them. It seems that Audacity can do this as well.
https://youtu.be/mlKX6p85R2M

Some software like iZotope RX and Nuendo can do "adaptive" noise reduction on the fly without capturing any profile. Depend on the characteristics of noise in the source files some methods may work better than the others.

Another problem I observed is this picture by the OP:
http://i.imgur.com/un5Ssau.jpg

The vertical lines over 16khz look like clipping done by converting lossy files to fixed point without applying replaygain beforehand.

Spectrals Question

Reply #7 –
Quote
Most vinyl comes from a digital source.
Most current  vinyl is from digital.      Most  vinyl records are old and were made before digital recording existed recording.

Spectrals Question

Reply #8 –
These were older records, so I don't think it has to do with lossy mastering.  Then again I have no idea what that would look like vs this.

So basically these were either recorded lossy and converted to wav, or he leaves his DJ mixer with a lpf on all the time?  I don't want to bug this guy over something so trivial, so I don't think I'll ever know the exact cause.

Guess I should just buy my own table.  Thanks everyone.