# Reading Tapes Backwards: A Legitimate Approach to Saving Time and Money in Digitization Projects?
## 2 Background  
There are several reasons why it can be advantageous to read a tape backwards in the context of audio preservation. At the project level: 1. to save time; 2. to save money. While these are desirable reasons to opt for this solution under most circumstances, they are not the only ones. There are other reasons at the preservation level:  
1. the tape only needs to be played once instead of twice or more: historical tapes are vulnerable and each pass is a stress for the tape, so one pass is less invasive than multiple passes;
2. saving time is not only interesting for the stakeholders, but it benefits the ultimate goal of preserving the audio heritage. Reducing the time necessary to complete one preservation project allows the team to focus on other preservation projects. The wealth of historical audio materials at risk of obsolescence and of irreversible loss stretches far beyond the resources that the audio community can currently deploy. Preserving the world's audio heritage is both a race against time and a goal that can only be achieved asymptotically. A reduction of time costs for each project increases our chance to preserve more of the collective audio heritage. These reasons make it appealing to adopt the'reverse' strategy in order to achieve a project's objectives more efficiently and not less effectively. However, there are also some disadvantages to consider at the methodological level:  
1. limitations in the monitoring of the signal transfer: digitizing multiple tracks on a two-sided tape at once means that monitoring can only be performed for some tracks at a time--depending on the flexibility of the setup. Isolating and monitoring only the track that is being read backwards may or may not allow the operator to make a good evaluation of the quality of the signal transfer;  
Figure 3: Example of track reversal. The top waveform is presented in the correct direction, where (**A**) is the start of the track and (**B**) is the end. Below, the same track reversed: (**B**) is at the beginning and (**A**) comes last. In this case, if we played the track, the human ear would perceive the sounds “backwards”. 2. the digital processing required to separate and revert the tracks after signal extraction come with their own time cost, plus they require specific tools and competences, and, finally, it needs to be performed correctly (non-zero chance of introducing errors into the workflow.) In general, the choice to read a tape backwards should be exercised with caution. This study aims to provide a better insight into the caveats of this decision, to help practitioners make informed decisions, and hopefully not wrong decisions. In any event, when this strategy is adopted, it should be explicitly reported in the preservation notes--including the operations that were subsequently applied to the signal in the digital workstation. When the tracks on a tape are picked up at once, they are processed in the digital workstation. It is important that the tracks be separated, linked correctly in the case of stereo signals, and that the tracks that were read backwards: 1. be reverted, heads to tail; and 2. their polarity (phase) be inverted as well. Reversion and inversion are linear operations that do not introduce unwanted alteration to the signal. The problem lies at the level of the tape head: how does a head behave when picking up a signal backwards, in the light of the 'analog behavior' that characterizes it? The next subsection provides a brief overview of magnetic recording to explain why, according to the theory, reading tracks backwards should not yield the same result as reading them in the intended direction. Electro-Magnetic Recording  
Magnetic tapes can be recorded and played by means of an electro-mechanic machine called a reel-to-reel tape recorder (see a simplified schema in Figure 4). During playback, the tape moves from left to right; from the source reel to the receiving reel.