Engine RPM for iPhone, version 2.4
- Engine RPM
is an iPhone app that listens to the sound of an engine and
calculates and displays the RPM of that engine from that
sound. The RPM range is 400-90,000 RPM. Engine configurations
include 2-cycle and 4-cycle up to 12 cylinders.
- You can find
the app in the App Store by clicking here:
- Here is what display
looks like. At the top in large digits is the calculated
RPM. The RPM value is calculated from the peaks in the
autocorrelation graph (in green at the bottom).
- Below that are
the hint controls, which specify the RPM range. By restricting
the search to a specific range of values, it is more likely that the
true engine sound can be found from amidst the background
noise. The hint is specified by a center value and a tolerance
value in percent. By swiping left or right in the blue bands
below the hint, you can adjust both the center RPM value and the
tolerance, which determines the minimum and maximum RPM values
- Instead of a
fixed hint band, you can also use tracking mode, which can
track RPM changes over the entire 400-90,000 RPM range. In
that mode the hint controls are replaced by a control that lets you
force the tracked RPM to be close the actual RPM so that true
tracking can begin.
- Below the hint
controls is a graph of the autocorrelation function. This
allows you to verify the reliability of the displayed RPM and it a
guide to adjusting the RPM range. The vertical yellow lines in
the graph correspond to periods in the sound produced by the
engine. If those yellow lines line up well with the peaks in
the graph, you can rely on the displayed RPM value.
- The conversion
from audio pitch to RPM depends on the engine configuration.
You can choose an engine configuration by specifying the number of
cylinders (up to 12) and whether the engine is a 2-cycle or 4-cycle
engine. You can also specify a generic factor that can
compensate for any gear ratio between the engine and the shaft whose
RPM you wish to display.
- Besides this
view, there are setup/configuration pages. Each page has it
own context-senstive help, which gives more information on how to
use the app. There is also a detailed Operations manual that can be downloaded from here.
- If you have any
questions about this app, you can e-mail us at: firstname.lastname@example.org