The Gain and Preamp settings for each channel both affect the amplitude of your recordings.
The preamplifier, controlled by the Preamp setting, and the main amplifier, controlled by the Gain setting, both increase the volume of the signal coming from the microphone before it is digitized. The difference between the two is where they are placed within the recording system.
The preamplifier is placed much closer to the microphone element and boosts the signal level before noise can be introduced from the rest of the SM5's electronics and from other sources. This improves the quality of the resulting signal, particularly in relatively quiet environments.
The primary gain setting has a more minor effect on audio quality but allows more fine adjustment of the resulting signal level.
Preamplifier Options
- Off
- On (default)
The Preamp setting is only available when using acoustic stub microphones. External microphones, such as the SMM-A2, have a similar preamplifier built into the microphone body that is always enabled.
The preamplifier adds 26 dB of gain to the acoustic stub microphones.
Gain Options
- 0.0 dB to 59.5 dB in 0.5-dB increments (16.0 dB default)
Reducing Gain to Avoid Clipping
The preamplifier and main amplifier both increase the volume level of a signal after it is picked up by the microphone and before it is turned into a digital recording. If too much volume amplification is applied to an already loud sound, the signal can be clipped at the top and bottom of the waveform.
If you find that the sounds you want to record frequently exhibit clipping, then you should reduce the total amplification. For the best audio quality, start by reducing the Gain setting. If you are recording extremely loud sounds that continue to clip even when Gain is set to 0 dB, then you should disable the Preamp and readjust Gain.
The spectrogram on the left simulates a signal recorded with the total Preamp and Gain amplification set too high, resulting in clipping, also called distortion or peaking. The spectrogram on the right shows the same signal recorded at a lower gain setting.
You can identify a clipped recording by making sure your viewer is not adding additional amplification. If the waveform reaches the upper or lower bounds of its range, then the signal is clipped. Clipping produces artificial harmonics and other artifacts that can make audio analysis difficult or impossible.
Increasing Gain to Improve Audio Quality in Extremely Quiet Environments
For most outdoor deployments, there is no benefit to increasing Gain above the default setting of 16 dB.
Increasing gain amplifies the volume of both the signal you want to record and the background noise of the surrounding environment; it does not improve the volume separation between the signal and noise. Increasing gain also raises the likelihood that wind or similar noise sources will create severe distortion that obscures other sounds.
In rare instances (such as a laboratory setting) where both the signal you want to record and the ambient noise are extremely quiet, increasing the gain can yield slightly better audio quality by using more of the SM5's dynamic range.