In the first place, one has to decide what task is before recording sound on the object. If it's just the detecting of the sound presence, for example - at night time in the shop - it will be most likely enough to use built-in microphone of the camera. If it's up to the speech recording and recognition - the task for the microphone is more difficult and its requirements are higher. In this case, one should consider using external microphones which will be connected to the Audio-In interfaces of camera (3.5 jack). Also, external mics will give the possibility to install them apart from the camera. We give next common recommendations for the montage and characteristics:
- Not recommended to set up external microphones on the ceiling, for it's like to gather the noises. Consider to place them on the wall at the human's height;
- Mounting microphones directly on the hard surfaces is not recommended, an additional layer of soft material should be considered;
- The external mic should be installed as far as possible from the constant noise sources;
- Not recommended to use power source of the impulse type for the external microphone (or one should consider using additional power source filter);
- Consider using only standardized PoE Splitter (which supports 802.af/at) to power up the external microphone;
- Consider using only shielded ethernet cable of FTP type if planned to use a PoE Splitter to power up the external microphone;
- The frequency bandwidth should be close to the human speech range, which is 70~450 Hz (could he higher - up to 1400 Hz);
- AGC (Automatic Gain Control) is not recommended to turn on;
- If planned to install the external microphone on the street, consider choosing the microphone with protection against the wind;
- Consider MEMS type microphones for the best quality or when the conditions are unknown;
- Don't forget to set up the audio settings on the camera itself - type of microphone (internal/external), codec (consider MP/AAC over G711), sampling frequency, etc.