The 15 kilocycle tone on Pepper
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Hi all, I am a bit intrigued by a part of Beatles music which can not, or hardly, be heard. When finishing Sgt. Pepper, The Beatles added some specialties. Think of the final piano chord, and of the gibberish in the concentric run-out groove. Between these two, at the suggestion of John, a high pitch tone was inserted, 'audible only for dogs'. (In fact, if your ears are still ok, you can hear it faintly). In The Complete Beatles Recording Sessions, Mark Lewisohn describes this on page 109 (21 April 1967). The interesting bit (well, for me) is that he says this effect was not on the master tape, but added at the disc cutting stage by Harry Moss, who cut (I think) all Beatles lp's. But: if this was not on the master tape, how was this done with later pressings (I know some US pressings lack this), as new pressings were done in the 1980's. How was this done with the cd's in 1987, and 2009? And with the recent lp-remasters? Is this the same tone, or was it done again? With Exact Audio Copy and Audacity on my pc I did a frequency analysis of this bit of Pepper, on the 1987 stereo, and 2009 stereo and mono cd's. The 15 kilocycle tone is there, in all cases. But is it the same as in 1967? Below is a comparison of the three, done some time ago. Sorry, it has Dutch axis descriptions. The peaks at other frequencies are artefacts of the method of analysis, but this shows the sound is there. http://1.bp.blogspot.com/-UQC3znhfSK4/UPcyLL-DX4I/AAAAAAAAGr8/NdKBdFzUfgM/s1600/spectrum.jpg
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I'm guessing that it was added to the master disc as a half-speed master, like a Chipmunks recording session, but with the waveform @ 7.5 KHz. Half speed mastering was also used in the 1970's to produce the CD-4 vinyl quad albums because the FM difference signal used to recover the discreet 4 channels was at around 44 KHz. It can't be cut to vinyl at normal speed, while tape rolls off at 19 KHz. typical. The 15 KHz. dog whistle may not have recorded correctly to tape due to the frequency rolloff characteristics of tape.
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Mark Lewisohn does not mention half-speed cutting this. You may be guessing right. I'm not sure if I understand what you say about roll-off frequency at 19 kHz of the tape, because it was not on the tape but added during cutting. That is what started me puzzling.
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A conventional audio tape speed uses a 19 KHz. bias frequency in order to boast the magnetic transfer of the tape head coils of the audio signal to tape. Any frequencies approaching that 19 KHz. bias may be distorted or may not record. This is strictly a phenomenon of recording tape. A faster tape recording, say for video tape, uses a higher bias frequency and either a faster tape speed or a spinning head against the tape to duplicate a faster tape speed without using more tape. On a side note, tape recording would be unusable without the use of the tape head bias frequency boosting the signal. Without it, the recording will sound violently distorted with gross malformations of the audio waveforms due to erratic fluctuations in the magnetic field. The bias helps maintain a constant magnetic field. Without using the bias frequency through a tape head during recording, only a preamp-to-tape head on a tape at 3 3/4 InchesPerSecond (I.P.S.), the audio will play back sounding like Neil Young's guitar on the electric version of "Hey Hey, My My (Into the Black). Max distortion.