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Lossy or Lossless? Please use this forum to post spectral and frequency analysis posts about shows you have your doubts about.

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  #1  
Old 2005-03-16, 10:40 PM
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Line at 15.5 on Spectral View - sourced from ?

I think I recall reading somewhere that a line at 15500 is the result of the audio being sourced from a TV signal. Can anyone confirm that?

(suspect pic attached)
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  #2  
Old 2005-03-16, 11:28 PM
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Re: Line at 15.5 on Spectral View - sourced from ?

29.970 fps x 525 lines = 15,734.2637 scan frequency.

That's the high pitched tone you always hear from your TV.
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  #3  
Old 2005-03-18, 04:24 AM
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Re: Line at 15.5 on Spectral View - sourced from ?

well put.
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  #4  
Old 2005-03-18, 04:47 AM
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Re: Line at 15.5 on Spectral View - sourced from ?

is this the same thing?

EDIT: oops cut off the end, the line is at the same as other one
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  #5  
Old 2005-03-18, 05:28 AM
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Re: Line at 15.5 on Spectral View - sourced from ?

yes.
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  #6  
Old 2005-03-18, 07:21 AM
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Re: Line at 15.5 on Spectral View - sourced from ?

I spent a fair amount of time yesterday looking more closely at this problem. The horizontal scan frequency (15,735) is only going to show up if the material was recorded with a microphone, not a line feed because it's an externally produced artifact, and not included in the broadcast signal. The FM pilot used in both radio & TV is 19kHz and the red line is below that frequency.

Working with CEP, I see that you must have a steady tone to produce this amount of spectral energy. Simply making a filter and boosting the frequency only amplifys already existing frequencies.

I can't match up this frequency with any parameters I know about (not saying too much) Anyone have other ideas ?? Could it be an artifact from some sort of Codec processing ?
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  #7  
Old 2005-03-18, 09:52 AM
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Re: Line at 15.5 on Spectral View - sourced from ?

I've been doing tape transfers and I get this bright line a fair amount of times from the tapes. Must have something to do with the equipment it was recorded on.
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  #8  
Old 2005-03-18, 10:50 AM
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Re: Line at 15.5 on Spectral View - sourced from ?

Quote:
Originally Posted by wazoo2u
I spent a fair amount of time yesterday looking more closely at this problem. The horizontal scan frequency (15,735) is only going to show up if the material was recorded with a microphone, not a line feed because it's an externally produced artifact, and not included in the broadcast signal. The FM pilot used in both radio & TV is 19kHz and the red line is below that frequency.

Working with CEP, I see that you must have a steady tone to produce this amount of spectral energy. Simply making a filter and boosting the frequency only amplifys already existing frequencies.

I can't match up this frequency with any parameters I know about (not saying too much) Anyone have other ideas ?? Could it be an artifact from some sort of Codec processing ?
It has something to do with TV. Try hooking your VCR up to your soundcard, what do you see? A red stripe. If you don't, try again with a cheaper soundcard and a cheaper VCR.
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  #9  
Old 2005-03-18, 11:40 AM
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Re: Line at 15.5 on Spectral View - sourced from ?

Quote:
Originally Posted by Lou
I've been doing tape transfers and I get this bright line a fair amount of times from the tapes. Must have something to do with the equipment it was recorded on.
I got a variation of this line on some tape transfers Tascam 424->iMac and I've seen faint but distinct lines on many boots with no TV or FM in the lineage.
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  #10  
Old 2005-03-18, 12:23 PM
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Re: Line at 15.5 on Spectral View - sourced from ?

Quote:
Originally Posted by Lou
I've been doing tape transfers and I get this bright line a fair amount of times from the tapes. Must have something to do with the equipment it was recorded on.
I'm thinking misaligned zenith. I gotta ask some of my tape tech colleagues. I distinctly remember that there can be artifacts like this from misaligned analog tape. It's possible that it can get recorded into the master and passed along in future gens. Unless all the errors of this type show up at the exact same frequency, I wouldn't generalize on the lineage.
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  #11  
Old 2005-03-18, 12:25 PM
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Re: Line at 15.5 on Spectral View - sourced from ?

Quote:
Originally Posted by Five
It has something to do with TV. Try hooking your VCR up to your soundcard, what do you see? A red stripe. If you don't, try again with a cheaper soundcard and a cheaper VCR.
What audio signal are you feeding into your soundcard when you see this ? AFM modulated "HiFi" audio, or the outputs of the longitudinal tracks ?
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  #12  
Old 2005-03-18, 03:21 PM
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Re: Line at 15.5 on Spectral View - sourced from ?

Quote:
Originally Posted by wazoo2u
What audio signal are you feeding into your soundcard when you see this ? AFM modulated "HiFi" audio, or the outputs of the longitudinal tracks ?
HiFi VCR (stereo rca outs) > soundcard

plese explain this "longitudinal" business

I've seen it with cassettes but the stripe is fainter, as ffooky says.

Generally, if the frequency response looks like FM and there's a fat bright red stipe at 15.5kHz, the source is probably TV. This should all be in the lineage, anyways!
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  #13  
Old 2005-03-18, 03:24 PM
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Re: Line at 15.5 on Spectral View - sourced from ?

In fact, the first of the two screenshots the stripe is quite faint, but the second sure looks like TV to me. Call it a hunch.
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  #14  
Old 2005-03-18, 04:15 PM
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Re: Line at 15.5 on Spectral View - sourced from ?

Quote:
Originally Posted by Five
HiFi VCR (stereo rca outs) > soundcard

plese explain this "longitudinal" business

I've seen it with cassettes but the stripe is fainter, as ffooky says.

Generally, if the frequency response looks like FM and there's a fat bright red stipe at 15.5kHz, the source is probably TV. This should all be in the lineage, anyways!
Without getting too involved, VHS (and Beta) Hi Fi recorders utilize both multiplex and traditional methods for recording audio. The "HiFi" signal is an FM modulated signal that's buried within the video signal (a longer tech explanation doesn't help here). The normal audio channels are recorded along the edge of the cassette tape (longitudinally) just like an audio cassette or reel to reel analog tape deck. The difference is that because the HiFi audio is tied to the video, you can't insert edit new video without losing that "tied" audio. The longitudinal tracks remain untouched.

The reason I'm asking is to see if the source audio error could be caused by a misaligned analog tape deck. The frequencies I see displayed in Spectral view don't match up to known pilot or scan frequencies. They're close, but they're not close enough to be considered deviations of those known freq's.
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  #15  
Old 2005-03-18, 04:54 PM
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Re: Line at 15.5 on Spectral View - sourced from ?

Maybe there's a bunch of misaligned VCRs out there. do you get the stripe when you hook your VCR up to your computer?

how about a screencap?
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