Concerning the correction of possible equalization errors found in tapes recorded on a machine running off of desired speed, we first must know the conditions under which that recording machine was calibrated. Because one first performs a playback response calibration, before performing the record calibration, it is of interest to know if the machine was running off-speed when the playback response curve was set (yes or no). Two different sets of conditions can follow from this. Yet we seldom (if ever) have such information about the recorder’s calibration. Andrew Hamilton: > by speeding up the playback machine to 15.2 ips - enough to > make the intended 1k tone actually play 1000 cps - does the > vari-sped playback (at the original record speed) magically > de-emphasize the haunted pre-emphasis? Yes, because the complementary record and playback equalizations are rooted in the frequency domain, they are (in a practical sense) blind to absolute tape speed and drift from nominal (and resulting changes to recorded wavelengths), provided those speed changes occur equally in BOTH recording and reproducing (playback). > What is the point at which an alteration should be made to > the pre- and/or de-emphasis EQ? Let's first simplify it by assuming there was no error introduced in the recorder's record equalization calibration by virtue of someone having first performed that machine's reproduce alignment with the machine running badly off speed. Then, there will be NO such point, IF the playback speed is matched to the record speed. Under this condition (which should always be the goal) the problems you are imagining disappear. Now, in the general case where the playback speed does NOT match the record speed, you are correct that a playback equalization (de-emphasis) tracking error will be introduced. As someone else responded, in most all practical examples experienced, this error is small enough to be negligible. > provided one had a way of dialing in the exact speed to make > the reproducer play back at the (actual) speed of the recorder You are correct to be emphasizing this, as it is one of the first things one needs to do in tape playback. Adjusting to known (or assumed) musical pitch, resolving to known (or assumed) recorded power line frequency hum, or possible other recorded pilot signal, including recording bias, are powerful tools for doing this. Fred Thal Audio Transfer Laboratory ATAE Studer