<html><head><title>Erasure problems, was Re: [ProAudio] Plangent playback, was: Re: FeralA - Recordings released encoded with Dolby A</title>
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<span style=" font-family:'Times New Roman'; font-size: 12pt;">Hello John,<br>
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see below<br>
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On Sunday, February 9, 2020 at 20:02, you (John Chester via ProAudio) wrote:<br>
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<td><span style=" font-family:'times new roman'; font-size: 12pt;">On 2/9/20 8:48 PM, Corey Bailey Audio Engineering via ProAudio wrote:<br>
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<td><span style=" font-family:'arial'; font-size: 12pt;">While I understand that you are capturing both signals during playback (on yet, a different machine), aren't you assuming that the record head & the erase head were in perfect agreement on the original record deck?</td>
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<span style=" font-family:'Times New Roman'; font-size: 12pt;">I comment in a previous reply that the "bias" probably erases and recorded erase signal.<br>
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<span style=" font-family:'arial'; font-size: 12pt;">The signal that remains on the tape is the bias signal from the record head, same head that's recording the audio. Thus, the bias and the audio on the tape have exactly the same azimuth and the same wow and flutter. </td>
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<span style=" font-family:'Times New Roman'; font-size: 12pt;">Certainly.<br>
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<span style=" font-family:'times new roman'; font-size: 12pt;">I don't know whether the erase head records a signal on the tape at the erase frequency.</td>
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<span style=" font-family:'Times New Roman'; font-size: 12pt;">On all of the older machines the bias frequency IS the erase frequency. On newer (Studer) machines, the erase frequency is 1/3 of the bias frequency, and they're locked together. Otherwise you get an audible beat (whistle that drifts around in frequency).<br>
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<td><span style=" font-family:'times new roman'; font-size: 12pt;"> -- I've never tried running a recorder with the record head disconnected. </td>
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<span style=" font-family:'Times New Roman'; font-size: 12pt;">It's not a good idea -- at least in the olden days, the "bulk erased" ("virgin tape") often was left with dc magnetization, which makes thumps and increased background noise, and also makes the recording sensitivity wander. I documented this in my "Erasure" paper in AES Journal. Do you know/remember that the duplication line that Irv had originally had no erasing heads. He complained to me about the 1 kHz recorded level<br>
wandering around. We found out that it was this problem. I forget which fix he applied, but he either carefully bulk erased all incoming tape stock; or machine erased it; or he put erasing heads on the duplicators.<br>
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<td><span style=" font-family:'times new roman'; font-size: 12pt;"> If the erase head does record the erase frequency, the bias is certainly strong enough to erase that signal.</td>
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<span style=" font-family:'Times New Roman'; font-size: 12pt;">I'd guess that there isn't much erase frequency recorded because it is grossly "overbiased".<br>
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<td><span style=" font-family:'times new roman'; font-size: 12pt;"> <br>
Playback is done with a head that's got wide enough bandwidth to capture both audio and bias with the same head. Because both signals are recovered by the same gap, flutter caused by the playback machine will be identical for audio and bias. Plangent processing will remove both the flutter of the recorder and the flutter of the playback machine.<br>
-- John Chester<br>
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<span style=" font-family:'calibri'; font-size: 9pt; color: #c0c0c0;"><i>-- <br>
Best regards,<br>
Jay McKnight <br>
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