Squelch and Gain

Introduction

In order to accomodate a wide range of audio inputs, we have added user configurable squelch (noise reduction) and gain controls for the '*' or volume reactive routines on the LED settings page.

Squelch

The volume reactive routines (starting with a single *), support a squelch or background noise suppression. For your current environment, , adjust this value on the LED Settings page so that the leds are only activated above a certain 'noise' level.

Gain

Line-in signals are typically much lower than that of some of the microphones. Rather than use an auto gain function, you can adjust the gain from 0 to 255, which translate to a 1.0 gain to a 5.0 gain for the volume reactive routines.

Tables of Approximate Values

For your microphone/line-in signal, adjust the squelch to reduce background noise and the gain settings in order to maximize the led activity. Gain values range from 0 to 255, which are 0 = 1.0, 64 = 2.0, 128 = 3.0, 192 = 4.0, 255 = 5.0

Calculation: sample = sample*sampleGain/64+sample;

FG085 Sinewave generator providing P-P output @ 100Hz. This generator does not provide pink or white noise capability. This is used to understand the voltages produced by various inputs. This table was used to configure an animation that reacted the same at different input levels.

Generator setting	Squelch	Gain	Comments
Line-In (FG085) 100Hz@ 4.0V	Sq: 5	Gain: 0	I don't want to go higher.
Line-In (FG085) 100Hz@ 2.4V	Sq: 5	Gain: 64	2X multiplier
Line-In (FG085) 100Hz@ 1.5V	Sq: 5	Gain: 128	3X multiplier
Line-In (FG085) 100Hz@ 1.1V	Sq: 5	Gain: 192	4X multiplier
Line-In (FG085) 100Hz@ 0.9V	Sq: 5	Gain: 255	5X multiplier

Using a pink noise generator from https://www.youtube.com/watch?v=WJ9Go1PnAVA

| Device | Squelch | Gain | Comments | :------------- | --- | --- | Line-In (Hyper-X Gaming Headset) | Sq: 5 | Gain: 255 | Goes to about 70% if everything is turned up to full. Uses 3.5mm output of USB based Hyper X gaming headset. | Line-In Laptop | Sq: 5 | Gain: 140 | A similarly tested laptop provided a significantly higher output voltage. | Line-In (Android) | Sq: 5 | Gain: 160 | Seems OK.

Providing ~80 dB of Pink noise to speaker from https://www.youtube.com/watch?v=WJ9Go1PnAVA

Microphone	Squelch	Gain	Comments
MAX9814 @60 dB	Sq: 25	Gain: 11	A noisy microphone configuration. Not recommended due to squelch setting.
MAX9814 @50 dB	Sq: 12	Gain: 63	A reasonable configuration.
MAX9814 @40 dB	Sq: 10	Gain: 112	A good configuration.
INMP401	Sq: 6	Gain: 64	I'd like to like this microphone, but have had a lot of bad ones (from China).
MAX4466 (midway)	Sq: 6	Gain: 82	This is a nice microphone that needs a bit of a boost.
MAX4466 (full CCW)	Sq: 6	Gain: 65	Seems OK.
MAX4466 (full CW)	Sq: 8	Gain: 110	Seems OK.
INMP441 (not yet integrated)	Sq:	Gain: 0	Wow! This thing is an amplification beast!

Conclusion: The INMP441 microphone has by far the widest dynamic range, but is also much more complex to configure and run.