Differences of ACI values between seewave and soundecology

The package seewave (Sueur et al. 2008) version 1.7.0 introduced the function ACI() to calculate the Acoustic Complexity Index (ACI). By then I was working on the last tests of my version of a function that would also calculate the ACI. So, I decided to keep my version in soundecology and let the community choose which version worked best for them.

The results of the functions do not match between the packages. I have received this question a few times, so I thought best to write a brief document about it since more people may wonder the same. After some tests, it seems that the differences are due to different assumptions or default values. The only way I can get the functions of both packages to agree was to set nbwindows in ACI() to a comparable value (duration of the file in seconds/seconds in each clump):

library(seewave)
library(soundecology)

data(tropicalsound)
duration <- length(tropicalsound@left)/tropicalsound@samp.rate # 20 seconds

duration

## [1] 20

ACI(tropicalsound, nbwindows=(duration/5))

## [1] 659.6697

acoustic_complexity(tropicalsound) # j is set to 5 by default

## 
##  max_freq not set, using value of: 11025 
## 
## 
##  min_freq not set, using value of: 0 
## 
## 
##  This is a mono file.
## 
##  Calculating index. Please wait... 
## 
##   Acoustic Complexity Index (total): 660.088

Another example

I also tried with a 50 second-long file (not included in this vignette):

sound1<-readWave("LINE_2003-10-30_20_00_34.wav")
duration <- length(sound1@left)/sound1@samp.rate # 50 seconds

ACI(sound1, nbwindows=(duration/5))
> 1566.69

acoustic_complexity(sound1) # j is set to 5 by default
> 1567.414

Changing the cluster size j to 10 sec:

ACI(sound1, nbwindows=(duration/10))
>783.8312

acoustic_complexity(sound1, j=10)
> 784.0986

The difference between the results from each package seems to come from how each function uses the clumping argument, j, which is set to 5 seconds as a default in both the SoundscapeMeter software and soundecology.

References

Sueur J., Aubin T., Simonis C. (2008). Seewave: a free modular tool for sound analysis and synthesis. Bioacoustics, 18: 213-226.

Vignette “Differences of ACI values between seewave and soundecology” by LJ Villanueva-Rivera

Version 1.0 (21 December 2015)