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In Reply to: RE: HDtracks 24/96 download vs same ripped from remastered CD.... posted by AbeCollins on July 10, 2014 at 09:17:51
Something's not right. I thought it could be the software used for creating the plot, but inmate rrob saw the same blip using different software. So we all suspected something in the music file causing the 28KHz blip.
But here I have more blips at 28KHz in totally different unrelated albums. The only common denominator I can think of is that they both came from HDtracks.
Led Zeppelin I 24/96 Download, track 01 "Good Times Bad Times"
60 Seconds sampled from the beginning of the track
The Doors L.A. Woman 24/96, track 05 "L.A. Woman"
60 Seconds sampled from the beginning of the track
This is weird. Here's an album track that I digitized myself at 24/96 using the HRT LineStreamer several months ago. No 28KHz blip like the HDtracks downloads of Led Zep and The Doors. Not sure what's going on here. Anyone have any ideas?
Velvet Underground home digitized from LP at 24/96, track 01 "Sunday Morning"
Follow Ups:
I just looked at a spectrum analysis of a commercial DVDA made from an analog tape master (LA4 Just Friends). Spike at 28.8 khz there as well. I am beginning to wonder if it isn't an artifact from the A to D process - or perhaps an artifact from noise reduction.
kerkula
Could there be code embedded in the 28kHz signal? Have you looked at the 28kHz signal in the time domain? Does it spell out HDTracks in some code every so often? Or is Jimmy really dead?
We need a like button on here.
True. But if it is a watermark, when e.g. HDTracks sees a file somewhere it shouldn't be, and runs it through their "decoder ring", it would easily spit out the answer.
They've gotta be doing something more than just putting "headers" into these files, too easily removed. Heck, they could encode an indirect link to the purchaser (somehow), which would make complete sense. But also not *at all* easy to do AFAIK and not affect playback, but there are probably encoding tricks and I sure wouldn't know of them. There have been much more theoretically complicated processes used to safeguard stuff (e.g. I know you remember the old one of laser-burning a hole in a FD in a uniquely encoded position).
I now suspect the tape machine(s) being used for playback and/or possibly record. I found another recording, Waltz for Debbie, that has the same 28 kHz blip.The mastering engineer for that transfer, Paul Stubblebine, might be able to shed light on this situation.
But note, I highly recommended the album in question and never looked at spectra at the time. :-)
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Are there tape machines in existence using signals in the 28kHz range, such as one might expect to find in a typical switching power supply? I figured all tape machines are so old they probably all use old school rectified, filtered, transformer isolated 60Hz supplies.
I'd be more inclined to suspect the digitizing machinery.
It's not uncommon to find PC power supplies switching in the 25KHz range but there's no set rule and it depends on the design. Switching power supplies can have a switching frequency upwards of 1-MHz.
I doubt that the old tape machines used switching power supplies. I was thinking it could be the tape bias frequency but I believe those were up around 400KHz.
No rule for sure but it makes passing emissions easier to keep frequencies down.
Unlikely to be digitizing machinery at least not in the Waltz for Debbie. That used the Pacific Microsonics ADC. It's unlikely that such a highly regarded device would have spuria that are 40 dB greater than spuria on my $150 juli@ sound card.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
I didn't see many details but am wondering what type of power supplies that Pacific Microsonics device uses. Undoubtedly it meets it's quoted specs but the question becomes how does any analog gear connected to it react to any emissions it may produce? especially old school analog gear which in it's day didn't require much immunity to perform well.
Abe as an example here is about a 20 second peak hold capture of my Asus Essence STX line input hooked up to my turntable and through my powered down phono preamps. I'm using Oscillometer free version to do the capture. I leave the preamps turned off during my noise hunts so as not to obscure the problems with preamp electronic noise.You can see my own setups noise imperfections quite clearly as I seem to have a similar spike at around 25kHz and what is likely to be it's second harmonic at around 50kHz. I'm pretty sure this is caused by my PC power supply but haven't had time to really figure it out. Since this gain is about what I'd use to capture and my particular noise problem is pretty small I might not worry about it so much considering the spike peak itself is somewhere around -115dB.
Edit: By the way in case you can't see the text this is with 2^14 points averaging and Blackman Harris window and with all weighting filtering shut off.
Second edit: I found it interesting that at 1:15 AM this morning my measurements with what I bellieve to be the same setting look quite different . Please see below. Perhaps theere is a power quality difference that explains it. It leads me to want to try some line filters. I don't believe I've noticed a drastic change like this before. Again only difference seems to be time. Notice how much lower than the apparent noise floor is with respect to the picture above. The noise spikes seem to be more or less the same but some new ones have been uncovered. such as at 1kHz which was buried in the noise before. Odd. Definitely going to need to dig into this effect deeper.
Edits: 07/12/14 07/12/14 07/12/14 07/14/14
Probably noise in the analog hardware used to make the original A to D rip. This is right in the frequency range where you might expect to find some switching noise from a typical power supply like you'd find in a PC for example. Though switchers are everywhere these days.
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