First you have to make sure heads are aligned properly which requires a great test tape to calibrate the playback system. Now some folks tamper with the playback equalization to put a HF hump at 15 or 16 KHZ to reach out a bit fiurther. Then you have to set your bias in the record mode to optimize the lowest distortion for your type of tape. Then and only then do you calibrate the record equalization to match the freq response of the playback curve. Remember you do this 10 db below the reference level of the capability of the tape your are using. Remember 3% distortion at 700 or 100 HZ is 6 db above the reference level and the record level is 10 db below that. Then you need either an External Dolby B or DBX deci-linear noise reduction system so you never record much above -6 db to prevent saturating your tape in the high frequencies. If your machine has bass bumps in the low frequency response then you don't use the DBX deci-linear system as it will over emphasize those bumps modulating the rest of the freq spectrum. You use the home version of the DBX system. My chief design engineer at the time tried using a model DBX 155 4 channel unit with his 3440 unit and had the issue. So he used two home type DBX units. As my Revox and professional Ampex studio machines were flat and 2 track or 4 channel 1/2 inch I used the DBX 157 units very successfully.
Note you really don't need response above 19,000 HZ or so. What you need is great signal to noise and low distortion at that frequency. Some thing you will never achieve using a 4 channel machine at 7.5 ips with 1/4 inch tape. Now Dolby and DBX will help quite a bit in fact. Besides most Quad records and phono cartridges and the decoders used at the time were all compromised anyway. That is why Dolby digital DVD's and processors became so popular so quickly. Because they all worked and anyone could easily hear that.
I will say when Maxell introduced their back coated XL series R2R tapes it allowed R2R machines to far surpass their original design specifications. But some Machines like professional Crown and Consumer Revox just could not record what the tape was capable of in its latest form. My A-77's couldn't and my HS 2 trk B-77 couldn't. Yet my old tube and early Ampex studio Machines could do so easily and why I kept them so long. I would record something on my SS AG 351 -2 or SS AG 300-2 and play back on the Revox B-77 and you could easily hear the compromised dynamics and the altered HF response. So get your self some kind of noise reduction gear or you are going to be very unsatisfied. Remember after Calibration -6db is the maximum recording level at 7.5 ips because Vu meters, even so called peak ones, lie.
