## 3 Problem Description  
Tape music is a genre of electroacoustic music in which the artwork coincides with the tape on which the audio signal is recorded [6]. In some cases, the composer did not provide a score; hence, the tape could be considered the final product of the creative process. The carrier has therefore a prominent role and must be considered in the philological analysis [18; 24]. The peculiarity of this type of analogue carrier is the possibility of editing the tape with several techniques. The main ones are introduced in [25], where the described techniques vary from straight recording to superimposition. Some of the main alterations considered in this paper are presented below. The editing consists on the physical alterations of the tape that is cut in pieces and then recomposed to obtain the desired sound or effect. Every piece is joined with the rest of the tape in a splice by using a strip of plastic coated with a thermal or pressure-sensitive adhesive called splicing tape [26]. As recommended in [27], the tape has to be cut at an angle of 45\({}^{\circ}\) to 60\({}^{\circ}\), measured with respect to the tape edge in order to avoid electrical disturbance. Without this disturbance, it is very difficult to find the slice by analyzing the audio track, and it could only be hypothesized if the audio content suddenly changes. In some cases, the splice does not join two pieces of magnetic tape, but one side consists of a leader-tape. It is a flexible plastic or paper strip that usually is spliced to either end of a roll of recording material [26]. In this case, the leader-tape extends the tape length in order to fasten the extremities of the tape to the hub of the flange and avoid wasting the magnetic tape that can be read entirely. In the creative process, the leader-tape is also important because it could be used inside the tape with several purposes, such as adding pauses or signaling new events or units. Silence parts could be also obtained by erasing previous recordings. The erasing head could be used to clean the tape before recording a new audio signal. Furthermore, as described in [25], a new signal could be recorded over the old one using superimposition. The result of these techniques is the sum of the two signals. In this paper, these techniques are generally referred to as overdubbing. All these alterations are irreversible and create new versions of the opera, which in philology are called witnesses. As outlined in the Introduction, this paper presents an innovative approach to the musicological analysis using phylogenetic techniques, typically adopted in forensics, in order to reconstruct the stemming codicum, which can be considered as an audio phylogenetic tree (APT) [17]. Nevertheless, the analysis is performed in the digital domain and not in the analogue one. This introduces a variable to the phylogenetic problem described in [17]: the digitization. An analogue tape can be read and digitized several times, creating similar digital versions of a unique document. These versions can differ from each other in the configuration of the tape recorder, in the quality of the Analog-to-Digital (A/D) converters and in the digital format on which the signal is saved. This study considers recorder configuration only, as the other options are not connected to the analogue carrier and thus not necessary in order to create a suitable model that takes into account the audio tape peculiarities. The most important parameter to be configured in the tape recorder during the listening and the digitization process is the replay speed. Six standard speeds are used: 30 ips (76.2 cm/s), 15 ips (38.1 cm/s), 7.5 ips (19.05 cm/s), 3.75 ips (9.525 cm/s), 15/8 ips (4.76 cm/s) and 15/16 ips (2.38 cm/s) [28]. The wrong choice of this parameter implies a time stretch and a pitch change that heavily distort the signal. To be thorough, this effect was used in electroacoustic music as a technique for altering the signal on purpose [25], but this aspect goes beyond the analysis of this work.