# Reading Tapes Backwards: A Legitimate Approach to Saving Time and Money in Digitization Projects?
## 4 Results and Discussion
### Contextual Notes on Phase Delay  
Phase delay in audio magnetic tape recording has been a well-known phenomenon in the expert community since before copying audio signals on tape was a necessity for preservation purposes. Phase delay caused by multiple sources is likely a major source of the mismatch between forward and reverse playback of the signals, based on the information presented in the next paragraphs. One of the first studies of this was conducted by [PERSON] and [PERSON] in 1965 [PERSON] and [PERSON] in 1965 [PERSON] and [PERSON] in 1965, where there was an attempt to maintain accurate transient response in a tape duplication system. Additional insight was offered by [33]. [PERSON] responded in 1968, citing an experiment he ran \"in 1951 or 1952\". \"After the original recording had been edited, a reverse re-recorded tape [copy] was made...During playback to air, I ran both tapes in synchronism and switched from \"A\" tape to \"B\" (reverse re-recorded) tape...Subsequent reports showed that in all cases the reverse-re-recorded tape was the most natural...The most noticeable improvement was in voice\" [34]. It was not until the 1970s and into the 1980s that the record phase distortion was addressed. In 1976, [PERSON] published a long tutorial and description of how the record circuits were developed for Ampex's final flagship audio recorder, the ATR-100. This offered a reduction in phase delay on the record side [35]. [PERSON] followed suit and, in 1982, issued a Product Information white paper describing modifications to the record amplifier for the A810 (which was also used in the A820) [36]. This was followed by \"Phase Compensation Design Considerations\" in their company journal, _SwissSound_[37]. In this paper, different types of record phase delay reduction are discussed, and they claim that what they are doing for the A810 is the finest yet. [PERSON] pointed out that the \"2 nd Version\" in the _SwissSound_ article [37] is the Ampex ATR-100 design, as shown on pages 6-43/44 in the ATR-100 service manual: \"IC A5, LM318 opamp, is the differentiator that gives the phase EQ that is summed into opamp A6 by way of rec EQ trim potentiometer R15/R18, high/low speed\" [38]. He also confirmed that the Sony APR-5000 uses the same record topology as the ATR-100. In addition, Otari did include record phase delay compensation in their MX80 machines (at least), and the 3M M23 had phase compensation on the playback side [39]. While the original circuit design in most of the earlier tape machines created a situation where, when a tape was played backwards on a similar machine, the phase delay of the reversed tape would partially mitigate the recording phase delays. Reducing the phase delay of the record process, as exemplified in the Ampex ATR-100, Studer A810/A820 and Sony APR-5000, could conceivably create an overshoot of correction with reverse playback, but this would only pertain to tapes made on these advanced machines. Tapes recorded in both directions are not professional master recordings, although undoubtedly important recordings that need to be preserved have been made in these formats. Bidirectional recordings were unlikely to be made on the late model recorders, which provided the reduced recording phase delay. Additionally, the recording polarity (as referenced to the acoustic polarity of the original signal) has not been rigorously standardized. Therefore, an argument can be made that, for important tapes where the utmost sound quality is paramount, one could make both forward and reverse copies, then make a reversed polarity copy of each (note that standard practice in making a reversed copy is to reverse both the direction and the polarity) and select the best sound from among the four copies. It is worth noting that complementary, compander-type noise reduction systems (Dolby, dbx, Telcom, and others) will not respond well to reverse playback, since they all rely on closely controlled time constants for proper operation and will not properly decode a signal that is reversed.