## 2 Materials and Methods  
### Recording  
EigenScape was recorded using the mh Acoustics EigenMike [27], a 32-channel spherical microphone array capable of recording up to fourth-order Ambisonic format. In [PERSON] Ambisonic microphone comparisons [28; 29] the EigenMike is among the lowest rated in terms of perceptual audio quality, rated as sounding \"dull\" compared to other microphones. Conversely, directional analysis shows the EigenMike gives the highest directional accuracy of any of the microphones tested, includingthe popular first-order Ambisonic Soundfield MKV and Core Sound TetraMic. It should be noted that the analysis in [28; 29] used only the first-order output from the EigenMike (for parity with the other microphones), disregarding the higher-order channels. Since the dataset presented in this paper is primarily aimed at machine (rather than human) listening, and the EigenMike can record far more detailed spatial information than first-order microphones whilst retaining a relatively portable form factor, the EigenMike was chosen for this task.  
Recordings were made using the proprietary EigenMike Microphone Interface Box and EigenStudio recording application [27]. Recordings were made at 24-bit/48 kHz resolution and the files use Ambisonic Channel Number (ACN) ordering [30]. All the recordings used a gain level of +25 dB set within the EigenStudio software as the ambient sound at many recording locations did not yield an adequate recording level at lower gain levels. The only exception to this is the recording labelled 'TrainStation-08', which used only +5 dB gain as very high level locomotive engine noise present at that location caused severe clipping at +25 dB.  
For the majority of the recordings, the EigenMike was mounted in a Rycote windshield designed for use with the SoundField ST350 microphone [31]. Although the windshield was not designed for the EigenMike, care was taken to rigidly mount the microphone and the shield was effective in cancelling wind noise. The first few recordings used a custom-made windshield, but this was switched for the Rycote as the set-up time proved far too long. One indoor recording did not use any windshield. The discrepancies in windshield use and gain level should be negligible by comparison to the wide variety of sounds present in the scenes, especially when coarse features are extracted for use in a machine listening system. Such a system should be robust to the small spectral changes incurred by use of different windshields and to differences in ambient sound level between scenes. Indeed, the DARES project [32] used entirely different recording setups for indoor and outdoor recordings and this was judged to have \"minimal influence on the quality of the database\". Nevertheless, these discrepancies are noted in metadata provided for EigenScape.  
To make these recordings, the microphone was mounted on a standard microphone stand set to around head height. A Samsung Gear 360 camera [33] was also mounted to the tripod, recording video in order to assist with future annotation of events within scenes where the sound might be ambiguous. Figure 1 shows the full recording apparatus.  
Figure 1: The setup used to record the EigenScape database: mb-Acoustics Eigenmike within a Rycote windshield, a Samsung Gear 360 camera, an Eigenmike Microphone Interface Box, and an Apple MacBook Pro. The equipment is shown here at Redcar Beach, UK: 54\({}^{\circ}\)37\({}^{\prime}\)16\({}^{\prime\prime}\) N, 1\({}^{\circ}\)04\({}^{\prime}\)50\({}^{\prime\prime}\) W.