Audio Engineering

Analog Tape Machine Alignment (6)

Record Alignment

The Music Telegraph | Text 2020/05/06 [13:42]
Audio Engineering

Analog Tape Machine Alignment (6)

Record Alignment

The Music Telegraph| 입력 : 2020/05/06 [13:42]

 

▲ Studer A80

© Reverb



Analog Tape Machine Alignment (6)

 

(Continued from previous article)

 

Record Alignment

The obvious standard to align the record electronics would be the same standard as the reproduce side, meaning the alignment tape. The only problem with this is that you cannot do a record alignment with a reproduce alignment tape. The very act of doing a recording will erase the tape. What you do is align the record side by using the tape machine's ability to reproduce a signal at the same time as it is recording it. This "read-after-write" capability will allow you to make adjustments to the record electro nics while observing and measuring the effects of those changes from the reproduce head. 

 

 

Bias

The bias frequency is a very high frequency sine wave (greater than 100 kHZ) that is added to the audio signal and sent to the record head. The purpose of the bias is to raise all the audio signal amplitudes above the non-linear section of the recording tape's hysterisis curve, ensuring that the recorded signal will be in the linear section. Without a sufficient and correct amount of bias current, you cannot have a clean, distortion-free recorded signal. Bias adjustment must be completed before any record level adjustments can be done.

 

To do a bias adjustment you record a high frequency sine wave (usually 10 kHz but not always) and adjust the bias level control while monitoring the reproduce output on the VU meter. There are a few different types of bias adjustment methods, but most common is the overbias adjustment done at 10 kHz. You will use this overbias method of adjustment.

 

 

Level Adjustment

The overall level of the record electronics is done with a 1 kHz sine wave. It is imposrtant to note that the bias must first be set correctly for your tape speed and formulation before conducting a level adjustment. If you change your recording speed or tape formulation, you must do another bias adjustment for these new parameters.

 

 

High Frequency Record Adjustment

As with the reproduce head, it is at the higher frequencies where head wear and gap width become critical factors in record head frequency response. A record level adjustment at 1 kHz will not tell you enough about the response at these higher frequencies, so another frequency in addition to the 1 kHz is needed. After doing a record level adjustment at 1 kHz you then do a highfrequency record adjustment using a 10 kHz signal. You do not readjust the reocrd level, but instead adjust the high frequency record equalization circuit to bring just that frequency range into calibration. 

 

 

 

 

 

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