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View Full Version : What does this drop around 20 kHz mean?


Luap
2010-05-29, 12:37 PM
Hello everyone.
I have some tracks with a frequency spectrum like the one in the Image.

What should I think of this? Is this track lossy or lossless? (For what it's worth, Audiochecker verifies these tracks as CDDA sourced)
Thanks.

Thulani
2010-05-29, 02:02 PM
Doesn't look loosy. You will also find many commercial albums that don't go above 20 khz.

AAR.oner
2010-05-29, 04:53 PM
looks like its from a TV source, due to the "spike" around 16kHz [pilot tone]

Luap
2010-05-29, 05:35 PM
I don't think my files are from a TV source...I think they originally are from a vinyl bootleg (Vigotone Smile - Beach Boys). (Btw, this is the only track with the 16 kHz spike I think).

@<hidden>: in the topic "MP3 (Lame 3.92) Spectral and Frequency analyses" there is a screen shot from a 256 kbit mp3 file that looks exactly the same as my file (drop around 20 kHz). How can you explain that?

showtaper
2010-05-29, 06:49 PM
I don't think my files are from a TV source...I think they originally are from a vinyl bootleg (Vigotone Smile - Beach Boys). (Btw, this is the only track with the 16 kHz spike I think).

@<hidden>: in the topic "MP3 (Lame 3.92) Spectral and Frequency analyses" there is a screen shot from a 256 kbit mp3 file that looks exactly the same as my file (drop around 20 kHz). How can you explain that?

That everyone is guessing (some better than others). There is no "foolproof"
way to tell if a file is lossy or not. Most software packages suck at detection.

Noise reduction, EQ, multiple tape generations, antique recording equipment and
many other things can make a recording appear suspect........

lintoni
2010-06-03, 04:42 AM
looks like its from a TV source, due to the "spike" around 16kHz [pilot tone]

Not necessarily TV sourced, but a TV may have been switched on nearby when somebody copied the recording.

http://www.solorb.com/dat-heads/digests/V3.100/D153#Msg2

eea123
2010-06-03, 06:42 AM
Not necessarily TV sourced, but a TV may have been switched on nearby when somebody copied the recording.

http://www.solorb.com/dat-heads/digests/V3.100/D153#Msg2

Wow, sounds like even a dedicated Hubbell outlet is prone to this. I don't know if you could even have your electrican pull the circuit(s) with a CRT to the opposite side / leg of your electrical panel and still avoid this?

Would use a decent AC line filter help?

paddington
2010-06-03, 09:44 AM
note:

- humans don't hear above 20kHz and CD players don't reproduce sound above that, on purpose. If you see a "drop" at 20kHz, there is nothing abnormal about that, at all. hardly anyone bothers to record higher than 20kHz.

- a 15kHz tone indicates FM Stereo broadcast, not TV. (TV pilot is much higher).

Since you say this came from vinyl directly, the noise here is most likely the noise coming from a CRT's badly shielded flyback during analog transfer. The horiz scan rate for a CRT is 15.734 kHz or so for NTSC.

In short, someone ran their unshielded cable too close to a CRT at some point in the transfer process (or the soundcard was picking it up from the CRT directly, if it was especially noisy). This is very common.

That's all. You can just notch filter it out and never notice. You can;t really hear anything at 15.734 kHz, anyway. If you think you have dog ears nd don't believe me, do a high pass filter from 15kHz-up and tell me what you hear.

It'll sound like quiet bugs fucking in the forest :thumbsup

lintoni
2010-06-03, 10:38 AM
note:

- humans don't hear above 20kHz and CD players don't reproduce sound above that, on purpose. If you see a "drop" at 20kHz, there is nothing abnormal about that, at all. hardly anyone bothers to record higher than 20kHz.

- a 15kHz tone indicates FM Stereo broadcast, not TV. (TV pilot is much higher).

Since you say this kHzcame from vinyl directly, the noise here is most likely the noise coming from a CRT's badly shielded flyback during analog transfer. The horiz scan rate for a CRT is 15.734 kHz or so for NTSC.

In short, someone ran their unshielded cable too close to a CRT at some point in the transfer process (or the soundcard was picking it up from the CRT directly, if it was especially noisy). This is very common.

That's all. You can just notch filter it out and never notice. You can;t really hear anything at 15.734 kHz, anyway. If you think you have dog ears nd don't believe me, do a high pass filter from 15kHz-up and tell me what you hear.

It'll sound like quiet bugs fucking in the forest :thumbsup

Wrong. FM pilot tone is at 19kHz (http://en.wikipedia.org/wiki/FM_broadcasting)

paddington
2010-06-03, 10:48 AM
:disbelief I'm sorry... too early. I was thinking of the FM audio cutoff, which is 15kHz.
I was also thinking about aural broadcast carrier for TV's offset, so i was wrong about that, too. Aaron was right.. the MTS TV tone is 15kHz.


The rest is correct ;)

need to head back to bed, apparently