Using Linux, in conjunction with a high-level sound card, and many available open source software allows to arrange inexpensive PAM (Passive Acoustic Monitoring) station able to operate 24/365 days. An implementation has been developed in 2014 and used for months in acoustic monitoring of marine mammals during oil and gas company related activities, in Adriatic Sea. The Linux operative system is commonly considered robust and able to provide high performance and reliability. Over the years it has been more and more used in audio applications, offering professional tools used both for professional (recording studios) and for scientific purpose. One of its more important sound component, in professional use, is Jack – Audio connection kit. Jack is an open source audio infrastructure that allows real-time, low-latency connections for audio devices between applications and vice-versa. Using Jack it is possible connecting a sound source (for example two or more hydrophones) to one or more specific signal processing modules, so the filtered sound can be returned to the headphones, and at the same time save the raw data to disk and show, always in real-time, the spectrogram on the display. AMS (Alsa Modular Synth) is a real-time modular synthesizer and effect processor. AMS gives different kind of modules really useful in PAM (Passive Acoustic Monitoring), avoiding the needs of analogic external devices, to equalize sound, apply bandpass filters and also divide the sound frequencies allowing, e.g. to listen cetacean clicks in real-time.