Input Display
Let's now look at the Input Display more thoroughly:
Clicking on the Channel Settings opens a pop-up menu that allows you to change all the
parameters of that channel. Everything you see in the input display and control window is
some of those parameters “exteriorized” so as to give you an “express access” to those
parameters on the fly. We will start by presenting those exteriorized parameters, and then
will systematically go through the channel settings menu.
Input channel identity shows you the current input channel. In order to see the entire
identity string, click the “long” button in the control panel.
The two led lights - green and red, are very important:
Recording Indicator: The green led, when turned on, tells you that the channel is
currently recording data into the hard disk. The behavior of the indicator depends on the
channel mode. For example, in an Active mode, the green light turns on when recording
is triggered by that channel.
Trimming Indicator: The red led light, when turned on, indicates trimming (bad news).
Trimming occurs when the channel input amplitude has reached the maximum value of
the digital recording range. Such recording is of bad quality and frequency distortions.
This is particularly an issue when the bird makes very loud calls and very soft songs. If
you are more interested in recording high quality songs, it is not a big deal if trimming
occurs while recording very loud calls.
Input
gain (yellow), Trigger threshold (red) & Display gain (blue)
Each channel has three color sliders: yellow (input gain), blue (display gain) and red
(peak threshold).
Input gain (yellow) slider Note: there is an accuracy (recording quality)
cost to changing
gain, but it is often low, or negligible when you change the gain by a few notches only. The input slider controls the gain of the channel, namely it can increase or decrease the
volume of the input signal. For example, turning it to 2 will give you wave file of twice
the intensity. If you find that you are trimming data (red light on) you can turn it down a
bit, or if you want to maximize gain, you can go up until trimming start occurring. We
generally recommend to keep the gain at or around 1, and instead, change signal
amplitude prior to digitization. This can be done either by your external amplifier (if you
have one) or by the control panel of your sound card (or of the NI card). To understand
the cost of using the gain control, consider the following example: in 16 bit recording, the
input signal is mapped into numbers ranging from 32,768 to -32,768. Now, if your signal
is weak compared to that range (say ranging from 3,200 to -3,200) and you then set input
gain to 10, then your signal will look loud in the wave file, since it covers the entire
digital range. However, this multiplying by 10 gives number in steps of 10, and in fact,
gives you a recording quality of about 12bit, instead of 16bit. If, on the other hand, you
amplify the input signal in the sound card control panel, you do not loose any accuracy.
Trigger threshold (red) slider set the threshold to trigger a recording session. When the
channel is recording, the threshold is shown as two dotted red lines in the oscilloscope
display, as shown in the earlier figures.
Display gain (blue) slider is the flip side of the peak threshold slider. It controls the gain
of the signal display and has no effect on the recorded signal. However, it does affect the
recording triggering just as the peak threshold slider does. For example, if you want to
record soft sounds it is more convenient (visually) to increase the peak gain than to
decrease the peak threshold.
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