MoTeC Knock OKM - Manual (Page 11)

MoTeC Configuration 11
Frequency Analysis
A competent tuner with the right equipment can measure and analyse the
knock frequency for the specific engine and associated hardware by
comparing the sound of the engine with and without detonation. Frequency
analysis will determine the theoretical best centre frequency. This is the
frequency where the difference of the engine sound with and without
detonation is most clear to detect.
Surprisingly minor changes to the engine hardware will affect the frequency of
the detonation “ring” throughout the structure. So frequency settings that suit
one car may not be suitable for another car of the identical model but with
slight modifications.
Warning
Knock frequency analysis is a specialised job, to be carried out
by experienced technicians. Incorrect operation can easily cause
severe engine damage.
Setup
1. Using the SKM tuning loom, connect an audio lead to the line in or
microphone in port on the PC.
The PC must be able to record sounds through a line in port and
simultaneously play it to the headphone jack, so the operator can
listen and monitor the engine while recording.
Note:
If your computer does not have the ability to record and listen
at the same time an alternative method should be used to listen to the
engine e.g. an external sound card or third party device.
2. Configure the PC to play sound only from the left channel. The right
channel is the knock window signal sent from the ECU.
Tip:
You can make an adapter plug for the headphones that joins the
sound from the left and right channel.
3. Connect audio headphones to the PC.
Tip:
To block out external engine and car noise, bud type ear phones
with high quality ear muffs used over top can be used.
4. To perform frequency analysis on the recorded audio file requires
dedicated software.
In this document Gold Wave software is used in all examples.
See Appendix 4 Gold Wave Settings