The PLEX KNOCK MONITOR V2 Explained in Quick Tips / PART 1: DSP Knock Signal Gain & Audio Pre-amplifier Gain – How to Configure?

Welcome to the first part of series of short articles explaining how the PLEX KNOCK MONITOR V2 works, by providing information on its inner workings and helpful tips on the installation and configuration. Both if you already own this device and if you are thinking of purchasing it, the provided information will help you understand how to make the most of our device and practically Never Miss Knock Again!

First Things First: How does it really work?

The PLEX KNOCK MONITOR V2 uses the signal from the knock sensor(s), in the following two parallel processes:

1. To detect knock using Digital Signal Processing (DSP)
2. To filter and amplify the signal for audio output

Now let’s go into more details on this:

1) Knock detection using DSP

For this function the signal is amplified/scaled using the Knock Signal Gain value (menu 2.3 & 2.4). A recommended starting value is “15”. So, should one change this value? It depends – for instance, if the knock signal output values average more than 120 units then it is recommended to decrease the signal gain value. Likewise, if the knock signal values  average less than “50”, then the signal gain value should be increased.

Briefly put, the variable knock signal gain makes the PLEX KNOCK MONITOR V2 suitable for most types of engines and is effectively used on commercial, racing, automotive, motorcycle, marine, snowmobile, off-road, truck and even industrial engines.

2) Filtering and amplification of the signal for Audio-out

The vibration signal that comes out of the knock sensor(s) and into the device, goes through 2 amplification stages. The first amplification takes place before processing and is controlled by the Audio Pre-amplifier Setting value (menu 5.5). The second amplification takes place after processing and is controlled by the Volume Adjustment knob (on the right side of the device). In most cases, the Audio Pre-Amplifier setting should be set at 0db.  Yet, on really noisy race engines the signal might need to be attenuated using a -9dB setting to prevent audio saturation (clipping).

In both cases, the Volume adjustment knob should be set so that the headphones output is comfortable for the user.

Key takeaways

1. Begin by ensuring that the Knock Signal Gain value is set to the recommended value of “15” (menu 2.3 & 2.4)
2. Decrease this only when the signal output values average > 120 units
3. Increase this only when the signal output values average <50 units
4. In most cases leave the Audio Pre-amplifier setting to 0db (menu 5.5)
5. In very noisy engines use a negative pre-amplifier gain setting (menu 5.5)

Visit the PLEX KNOCK MONITOR V2 product page.

Order the KNOCK MONITOR here.

Sign-up for More Tips & Tricks!