How to calibrate the FM dolby and bias?

[MCS Guy]

On my Realistic (hitachi D-850), It has regular recording level knobs and Dolby calibration thumbwheels in the front. In the back, There is a another set of adjustments for FM dolby calibration and a Bias Fine adjustment. The deck also has a built in test tone. I also Have a Rec level check on my receiver.

The deck sounds pretty good now, but I want to get the best I can. How do I go about setting all the adjustments properly?

 

[OvenMaster]

IMHO, don't waste your time on FM Dolby adjustments... there aren't any more FM Dolby broadcasts. They were all finished by the mid-80's. Just make sure that if you have a de-emphasis selector anywhere, set it on 75 microseconds, which is the US FM broadcast standard. 25 microseconds was used for Dolby FM only.
Tom

 

[goldear]

The Dolby FM Calibration should be completely ignored. That has nothing to do with playing or recording tapes, and it is not used anywhere anymore.

Now, on the other hand, the other front-panel Dolby calibration controls, and the fine bias control are extremely useful. Do not confuse the Dolby FM calibration with the Dolby NR calibration; these are completely unrelated.

I'm too tired to write up a detailed callibration procedure for you at the moment though. But I will give you a couple of pointers. This is very easy to do with a 3 head machine, but is a real pain for two head machines.

Basically, you need to adjust the Dolby calibration controls so that when you are recording a test tone on a tape, that it plays back at the Dolby level on you VU meters. This adjusts your record sensitivity.

Next you need to listen to the recorded tape to a recording with a lot of highs in it. If the tape sounds a bit duller than the source, then decrease the bias slightly. If the tape sounds too bright, then increase the bias slightly. The goals is to achieve esentially flat frequency response, and to get proper dolby "tracking".

 

[MCS Guy]

Basically, you need to adjust the Dolby calibration controls so that when you are recording a test tone on a tape, that it plays back at the Dolby level on you VU meters.

OK, Im a little confused. what the dolby level?

I thought I set the recording level to the source level. I was taking the test tone and recording it on tape and setting the level between the source and the tape exactly the same.

 

[goldear]

Sorry, I should have been a little more clear.

The dolby level is where your VU meter's usually have a little Dolby "double D" marking on them (if you've ever wondered what that was for, then now you know!). That represents the industry standard "dolby level". On really good machines this often corresponts to "0 dB" on the VU meters, but sometimes it is at a different level like "+3 db".

Yes, the goal is to compensate for tape sensitivity; so achieveing the same tape and source levels is the general goal. However, I would suspect that the unit proably records this tone at about 0dB, which is often (but not always) the dolby level.