# A Collection of Best Practices for the Collection and Analysis of Bioacoustic Data
## 8 Discussion
If the population of interest is only in a certain location at some times of the day or year, one must consider whether placing a recorder in that location will bias results. On the other hand, if an acoustic study is more broad scale, one must decide how many recorders are necessary. This decision should be based on the distance over which sounds of interest can be detected, which in turn will be influenced by the sounds produced (frequency, source level, etc. ), the environment through which those sounds will travel, and the sensitivity of the recording equipment being used. Hand-in-hand with this is the need for balanced geographic coverage across study strata. If the study covers a large area, the researcher must consider how to achieve balanced coverage and/or whether certain areas within the larger area are more important to monitor than others. Finally, one should consider transducer placement with regard to their species of interest; for example, placing transducers at different heights in a tree or depths underwater will affect which species' signals are recorded and what types of noise interference or propagation effects may result. The resulting placement should optimize the signal to noise ratio for the sounds of interest. Another factor that needs consideration is that acoustic studies often involve the use of multiple transducers placed in different locations and/or at different times. If multiple transducers are being used, the extent of overlap among transducers must be evaluated. For example, in Section 3, Ecosystem Biodiversity, [PERSON] et al. [69] positioned microphones at least 300 m from each other to limit the probability of detecting given sounds on multiple microphones. In other situations, for example when acoustic localization is desired, transducers should be placed so that target sounds are detected on multiple transducers. In one such example, in Section 6 Predator-prey relationships, [PERSON] et al. [72] used hydrophones spaced 30 cm apart, which allowed acoustic localization of harbor porpoise clicks. When using multiple transducers in a study it is important to ensure they are time synchronized, and use the same sensitivity and frequency responses, high/low frequency pass filters, and sampling rates. Yet, another consideration involves the frequency response of the transducers and the frequency range of the signals of interest. When making decisions about recording equipment, one must be familiar with the sounds of interest to ensure that the equipment is capable of capturing the entire frequency range required. For example, when recording narrowband high frequency clicks produced by species such as harbor porpoises, it is necessary to use hydrophones that have frequency responses to at least 150 kHz, and to record using a sampling rate of at least 300 kHz. Any signal with frequencies over one-half of the sampling rate, commonly called the Nyquist frequency [110], will be biased by aliasing; therefore, for sounds to be accurately represented in recordings, a sampling rate that is at least twice that of the highest frequency sound of interest must be used. If equipment limitations necessitate a lower-than-optimal sampling rate, an analog anti-aliasing filter needs to be implemented to avoid aliasing from uncaptured higher frequency components. Once decisions have been made regarding the type and placement of recording equipment and the recording schedules, one must give careful thought to the supplemental data and observations (e.g., metadata) that will be collected along with the acoustic recordings. There are many factors that can affect the quality of acoustic recordings, the sounds that are detected, and the interpretation of the data collected, and it is crucial to document these factors along with all recordings where possible. The type of supplemental data required will vary with the aims and scope of each study.