Synthesize sounds

We often want to figure out how transmission properties vary across a range of frequencies. For instance, Tobias et al (2010) studied whether acoustic adaptation (a special case of sensory drive; Morton 1975), could explain song evolution in Amazonian avian communities. To test this the authors created synthetic pure tone sounds that were used as playback and re-recorded in different habitats. This is the actual procedure of creating synthetic sounds as they described it:

“Tones were synthesized at six different frequencies (0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 kHz) to encompass the range of maximum avian auditory sensitivity (Dooling 1982). At each frequency, we generated two sequences of two 100-msec tones. One sequence had a relatively short interval of 150 msec, close to the mean internote interval in our sample (152± 4 msec). The other sequence had a longer interval of 250 msec, close to the mean maximum internote interval in our sample (283± 74 msec). The first sequence reflects a fast-paced song and the second a slower paced song (sensu Slabbekoorn et al. 2007). The master file (44100 Hz/16 bit WAV) thereby consisted of a series of 12 pairs of artificial 100-ms constant-frequency tones at six different frequencies (0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 kHz).”

We can synthesize the same pure tones using the function synth_sounds(). The function requires 1) the frequencies of tones to synthesize (argument frequencies, in kHz) and 2) the duration of the tones (durations, in seconds). In addition, logical arguments fm and am allow to create frequency and amplitude modulated sounds respectively. In our case we need six tones of 100 ms at 0.5, 1, 2, 3, 4, and 5 kHz separated by intervals of 150 ms (at least for the first synthetic file described in Tobias et al 2010). We can also get a selection table (sensu warbleR) with the information about the time and frequency location of every sound. This would be required in order to make the master sound file. To get the selection table we need to set the argument selec.table = TRUE. This can be done as follows:

# load packages
library(viridis)

Loading required package: viridisLite

library(baRulho)

Loading required package: warbleR

Loading required package: tuneR

Loading required package: seewave

Loading required package: NatureSounds

Loading required package: ohun

Please cite 'ohun' as: 

 Araya-Salas, M., Smith-Vidaurre, G., Chaverri, G., Brenes, J. C., Chirino, F., Elizondo-Calvo, J., & Rico-Guevara, A. 2023. ohun: an R package for diagnosing and optimizing automatic sound event detection. Methods in Ecology and Evolution. https://doi.org/10.1111/2041-210X.14170

Please cite 'baRulho' as: 

Araya-Salas M., E. Grabarczyk, M. Quiroz-Oliva, A. Garcia-Rodriguez, A. Rico-Guevara. (2023), baRulho: an R package to quantify degradation in animal acoustic signals .bioRxiv 2023.11.22.568305.

Attaching package: 'baRulho'

The following object is masked from 'package:seewave':

    attenuation

library(Rraven)

# synthesize
synth_est <- baRulho::synth_sounds(
  mar = 0.1,
  frequencies = c(0.5, 1:5),
  durations = 0.1,
  fm = FALSE,
  am = FALSE,
  sampling.rate = 12
)

synthesizing sounds (step 0 of 0):

# convert into a single wave object
synth_wav <- Rraven::exp_est(X = synth_est,
                             single.file = TRUE,
                             wave.object = TRUE)


# plot spectro
seewave::spectro(
  wave = synth_wav,
  scale = FALSE,
  palette = viridis,
  grid = FALSE,
  collevels = seq(-20, 0, 1),
  osc = TRUE,
  colwave = "#31688EB3",
  heights = c(2, 1),
  wl = 100
)

The function can add complexity to additional acoustic dimensions. For instance the following code generates all possible combinations of frequencies (2, 3 and 4 kHz), durations (0.1, and 0.2 s), frequency modulation (tonal and modulated) and amplitude modulation (flat and modulated envelope):

# synthesize
synth_est2 <- baRulho::synth_sounds(
  mar = 0.01,
  sig2 = 0.05,
  frequencies = 2:4,
  durations = c(0.1, 0.2),
  fm = TRUE,
  am = TRUE,
  shuffle = TRUE,
  seed = 123,
  sampling.rate = 12
)

# convert into a single wave object
synth_wav2 <- Rraven::exp_est(
  X = synth_est2,
  single.file = TRUE,
  path = tempdir(),
  wave.object = TRUE
)

# plot spectro
seewave::spectro(
  synth_wav2,
  tlim = c(0, 2),
  scale = FALSE,
  palette = viridis,
  grid = FALSE,
  collevels = seq(-20, 0, 1),
  osc = TRUE,
  colwave = "#31688EB3",
  heights = c(2, 1),
  wl = 140
)

Note that the output is an extended selection table that contains the time-frequency annotations for all synthetic sounds:

# check first 6 rows
head(as.data.frame(synth_est2))

As this is an extended selection table, the ‘sound.files’ column refers to Wave objects included as attributes instead of files in a directory:

# check name of wave objects
names(attributes(synth_est2)$wave.objects)

 [1] "synthetic_sound_1"  "synthetic_sound_2"  "synthetic_sound_3"  "synthetic_sound_4" 
 [5] "synthetic_sound_5"  "synthetic_sound_6"  "synthetic_sound_7"  "synthetic_sound_8" 
 [9] "synthetic_sound_9"  "synthetic_sound_10" "synthetic_sound_11" "synthetic_sound_12"
[13] "synthetic_sound_13" "synthetic_sound_14" "synthetic_sound_15" "synthetic_sound_16"
[17] "synthetic_sound_17" "synthetic_sound_18" "synthetic_sound_19" "synthetic_sound_20"
[21] "synthetic_sound_21" "synthetic_sound_22" "synthetic_sound_23" "synthetic_sound_24"

Create master sound file for playback

The function master_sound_file() creates a master sound file (as you probably guessed) for playback experiments. The function takes wave objects from an data frame or (extended) selection table containing the model sounds and concatenates them in a single sound file (with some silence in between sounds which length can be modified). master_sound_file() adds acoustic markers at the start and end of the playback that can be used to time-sync re-recorded sounds, which streamlines quantification of acoustic degradation. The following example shows how to create a master sound file using the synthetic sounds generated above. For the synthetic sounds we need to add a little space between the top and bottom frequency because sim_songs() make those values exactly the same for pure tones:

# create master sound file
synth_master_annotations <- baRulho::master_sound_file(
  X = synth_est,
  file.name = "synthetic_master",
  dest.path = tempdir(),
  gap.duration = 0.15
)

The file synthetic_master.wav has been saved in the directory path '/tmp/RtmpzGOHO2'

The function saves the master sound file as a wave file and returns a selection table in the R environment with the time and frequency ‘coordinates’ of the sounds in that file (be careful when playing the master sound file as it can be shocking for some audiences!). We can look at the spectrogram of the output file using the seewave function spectro() as follows:

# read wave file
wave <-
  tuneR::readWave(file.path(tempdir(), "synthetic_master.wav"))

# plot spectrogram
seewave::spectro(
  wave,
  scale = FALSE,
  palette = viridis,
  wl = 150,
  grid = FALSE,
  flim = c(0, 4.7)
)

The function can also create a master sound file from sounds found in sound files and from several sounds files, as is likely the case with recordings collected in the field. The following example shows how to create a master sound file using several sound files. The code uses the example data and recordings from the package warbleR:

# load example data from warbleR
data(list = c(
  "Phae.long1",
  "Phae.long2",
  "Phae.long3",
  "Phae.long4",
  "lbh_selec_table"
))

# save sound files to temporary folder
writeWave(Phae.long1, file.path(tempdir(), "Phae.long1.wav"))
writeWave(Phae.long2, file.path(tempdir(), "Phae.long2.wav"))
writeWave(Phae.long3, file.path(tempdir(), "Phae.long3.wav"))
writeWave(Phae.long4, file.path(tempdir(), "Phae.long4.wav"))

# make an extended selection table
est <- warbleR::selection_table(
  X = lbh_selec_table,
  extended = TRUE,
  path = tempdir(),
  pb = FALSE
)

all selections are OK 

# add sound_id column
est$sound.id <- paste0(abbreviate(est$sound.files), est$selec)

# create master sound file
master_annotations <- baRulho::master_sound_file(
  X = est,
  file.name = "example_master",
  dest.path = tempdir(),
  gap.duration = 0.3
)

The file example_master.wav has been saved in the directory path '/tmp/RtmpzGOHO2'

Again, we can look at the spectrogram of the output file:

# read wave file
wave <-
  tuneR::readWave(file.path(tempdir(), "example_master.wav"))

# plot spectrogram
seewave::spectro(
  wave,
  scale = FALSE,
  palette = viridis,
  collevels = seq(-120, 0, 5),
  wl = 500,
  grid = FALSE,
  flim = c(0, 10)
)

Note that the output could also be exported to Raven sound analysis software (Cornell Lab of Ornithology) for visualization or further manipulation using the function exp_raven() from the Rraven package. exp_raven() exports selections in the R environment to a ‘.txt’ file that can be read in Raven:

Rraven::exp_raven(master_annotations, path = tempdir(),
                  file.name = "example_master_selection_table")

Both sound files and annotations can be visualized in Raven ( acoustic analysis software):

knitr::include_graphics("example_master_table.jpg")

Take a look at the Rraven vignette for more details on how to export and import data from R to Raven.

Note that the start and end markers are placed at relatively low frequencies so they are less affected by degradation. The frequency range of markers can be set with argument flim. The relative amplitude of markers can also be adjusted with the amp.marker argument. Amplitude of markers will be multiplied by the value supplied so markers will be louder than sounds. These two features should increases the chances of detecting the markers at further distances.

Align re-recorded sounds

Once we went to the field (or lab) and re-recorded the master sound files at different distances, we are ready to start with data analysis. The first step for getting the data ready for analysis involves finding sounds within the re-recorded sound files. We only need to align the start marker between the master playback and the re-recorded sound files, based on the fact that the time difference between the marker and the sounds should be the same in both cases:

We will use acoustic data included in the package as example data. This is a data subset from a sound transmission experiment. The complete data set of the experiment is hosted in this repository. There are two example objects that will be used:

data("master_est")

data("test_sounds_est")

These are the files contained in the data set:

unique(master_est$sound.files)

[1] "master.wav"

unique(test_sounds_est$sound.files)

[1] "10m_closed.wav" "10m_open.wav"   "1m_open.wav"    "30m_closed.wav" "30m_open.wav"  

Their names are self-explanatory: a master sound file (“master.wav”) and its annotations, a reference sound file (“reference_1m.wav”) and two test files (“test_10m.wav” and “test_20m.wav”) re-recorded at 10 and 20 m respectively.

Now we will save those files in a temporary working directory (those objects are extended selection tables in the R environment) to resemble the usual case in which the acoustic data is found in sound files.

# first remove any other wave file in the temporary working directory (dont do it with your data!)
unlink(list.files(
  path = tempdir(),
  full.names = TRUE,
  pattern = ".wav"
))

# save master sound file
writeWave(object = attr(master_est, "wave.objects")[[1]],
          file.path(tempdir(), "master.wav"))

# save test sound files
for (i in unique(test_sounds_est$sound.files)) {
  writeWave(object = attr(test_sounds_est, "wave.objects")[[i]], file.path(tempdir(), i))
}

# make annotations a data frame
master_annotations <- as.data.frame(master_est)

The annotations needed for aligning test sound must share the following structure:

master_annotations

Note the ‘sound.id’ column which contains a unique identifier for each sound. This will be used to label their counterparts in the test sound files. Users can import annotations from Raven using the Rraven package (see this vignette).

To find the location of the start marker on the test sound files we use the functions find_markers() to run a cross-correlation of one or more markers across the test files in order to determine the exact time in which each marker is found:

markers_position <-
  baRulho::find_markers(X = master_annotations, path = tempdir())

markers_position

The position of the markers is determined as the highest spectrogram cross-correlation value for each marker using the functions find_markers(). If two or more markers are used the function computes an additional column, ‘time.mismatch’, that compares the time difference between the two markers in the test files against that in the master sound file. In a perfect detection the value must be 0. So this number can be used as a measure of error. In some cases precision can improve by increasing the time resolution of the spectrogram, that is, by lowering the size of the time window. This is done with the argument ‘hop.size’. By default it is 11.6 ms (which is equivalent to a 512 samples window length in a 44.1 kHz file). Let’s try 4 ms:

# lower window length
markers_position <-
  baRulho::find_markers(X = master_annotations,
                        hop.size = 4,
                        path = tempdir())

markers_position

With the time location of acoustic markers we can infer the position of all other sounds in the new recordings. A selection table from re-recorded files can be generated using the function align_test_files():

aligned_tests <-
  baRulho::align_test_files(
    X = master_annotations,
    Y = markers_position,
    by.song = TRUE,
    remove.markers = FALSE,
    path = tempdir()
  )

The function returns an object of the same class of the input object ‘X’. In this case ‘X’ is an data.frame:

is.data.frame(aligned_tests)

[1] TRUE

aligned_tests

We can check the precision of the alignment by looking at the spectrograms. The function plot_aligned_sounds() can create spectrograms to visually inspect alignment precision on test sound files. The spectrograms are saved as individual JPEG image files (in ‘dest.path’ if supplied). One file is created for each sound file:

aligned_imgs <- baRulho::plot_aligned_sounds(
  X = aligned_tests,
  path = tempdir(),
  dest.path = tempdir(),
  duration = 2.4,
  ovlp = 0
)

The image files have been saved in the directory path '/tmp/RtmpzGOHO2'

aligned_imgs

[1] "/tmp/RtmpzGOHO2/plot_align_10m_closed.jpeg" "/tmp/RtmpzGOHO2/plot_align_10m_open.jpeg"  
[3] "/tmp/RtmpzGOHO2/plot_align_1m_open.jpeg"    "/tmp/RtmpzGOHO2/plot_align_30m_closed.jpeg"
[5] "/tmp/RtmpzGOHO2/plot_align_30m_open.jpeg"  

These are two of the files generated by the code above:

baRulho::manual_realign(
  X = aligned_tests,
  Y = master_annotations,
  duration = 2.4,
  path = tempdir()
)

Further aligning

When alignments are done manually (or when broadcasting devices add some short delays as the case of some bluetooth transmitters) there could be some small misalignment between the inferred versus the actual start time of re-recorded sounds. This is problematic for quantifying degradation in baRulho (and other sound analysis software) as precise alignment of sound is crucial for the accuracy of downstream measures of sound degradation.

Misalignment can be fixed with the function auto_realign(). This function uses spectrogram cross-correlation to sync the position in time of sounds with regard to a reference sound. manual_realign() takes the sound recorded at the closest distance to the source as the reference sound. The function calls warbleR’s cross_correlation() (just as we did above) internally to align sounds using cross-correlation. We can simulate a aligned data set in which test sound are slightly off their position:

  data("test_sounds_est")
  data("master_est")
  
  # create "unaligned_test_sounds_est" by
  # adding error to "test_sounds_est" start and end
  unaligned_test_sounds_est <- test_sounds_est
  set.seed(123)
  noise_time <- sample(c(0.009, -0.01, 0.03, -0.03, 0, 0.07, -0.007),
  nrow(unaligned_test_sounds_est),
  replace = TRUE)
  
  attr(unaligned_test_sounds_est, "check.res")$start <- 
  unaligned_test_sounds_est$start <- 
  unaligned_test_sounds_est$start + noise_time
  attr(unaligned_test_sounds_est, "check.res")$end <- 
  unaligned_test_sounds_est$end  <- 
  unaligned_test_sounds_est$end + noise_time

Now we can re-aligned test sounds:

#re align
rts <- auto_realign(X = unaligned_test_sounds_est, Y = master_est)

This is how the sounds look before and after being aligned:

 

In case this doesn’t work as expected there is another option. The function seltailor() from warbleR allows user to manually adjust the start and end of sounds in a extended selection table. Alternatively, users can manually determined the position of the the markers using Raven and then import the annotations into ‘R’ using the function ‘imp_raven()’ from the Rraven package.

 

---

Please report any bugs here.

The package baRulho should be cited as follows:

Araya-Salas, M. (2020), baRulho: quantifying degradation of (animal) acoustic signals in R. R package version 1.0.0.

---

References

1. Araya-Salas, M. (2017). Rraven: connecting R and Raven bioacoustic software. R package version 1.0.0.

2. Araya-Salas, M. (2020), baRulho: quantifying degradation of (animal) acoustic signals in R. R package version 1.0.0

3. Araya-Salas M, Smith-Vidaurre G. (2017) warbleR: An R package to streamline analysis of animal acoustic signals. Methods Ecol Evol 8:184–191.

4. Dabelsteen, T., Larsen, O. N., & Pedersen, S. B. (1993). Habitat-induced degradation of sound signals: Quantifying the effects of communication sounds and bird location on blur ratio, excess attenuation, and signal-to-noise ratio in blackbird song. The Journal of the Acoustical Society of America, 93(4), 2206.

5. Marten, K., & Marler, P. (1977). Sound transmission and its significance for animal vocalization. Behavioral Ecology and Sociobiology, 2(3), 271-290.

6. Morton, E. S. (1975). Ecological sources of selection on avian sounds. The American Naturalist, 109(965), 17-34.

7. Tobias, J. A., Aben, J., Brumfield, R. T., Derryberry, E. P., Halfwerk, W., Slabbekoorn, H., & Seddon, N. (2010). Song divergence by sensory drive in Amazonian birds. Evolution, 64(10), 2820-2839.

Session information

R version 4.4.2 (2024-10-31)
Platform: x86_64-pc-linux-gnu
Running under: Ubuntu 24.04.1 LTS

Matrix products: default
BLAS:   /usr/lib/x86_64-linux-gnu/openblas-pthread/libblas.so.3 
LAPACK: /usr/lib/x86_64-linux-gnu/openblas-pthread/libopenblasp-r0.3.26.so;  LAPACK version 3.12.0

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=en_US.UTF-8       
 [4] LC_COLLATE=C               LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                  LC_ADDRESS=C              
[10] LC_TELEPHONE=C             LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

time zone: Etc/UTC
tzcode source: system (glibc)

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] Rraven_1.0.14      baRulho_2.1.2      ohun_1.0.2         warbleR_1.1.32     NatureSounds_1.0.4
 [6] seewave_2.2.3      tuneR_1.4.7        viridis_0.6.5      viridisLite_0.4.2  knitr_1.48        
[11] rmarkdown_2.29    

loaded via a namespace (and not attached):
 [1] gtable_0.3.6        rjson_0.2.23        xfun_0.49           bslib_0.8.0        
 [5] ggplot2_3.5.1       vctrs_0.6.5         tools_4.4.2         bitops_1.0-9       
 [9] parallel_4.4.2      tibble_3.2.1        proxy_0.4-27        fansi_1.0.6        
[13] highr_0.11          pkgconfig_2.0.3     KernSmooth_2.23-24  checkmate_2.3.2    
[17] lifecycle_1.0.4     stringr_1.5.1       compiler_4.4.2      brio_1.1.5         
[21] munsell_0.5.1       htmltools_0.5.8.1   sys_3.4.3           buildtools_1.0.0   
[25] class_7.3-22        sass_0.4.9          RCurl_1.98-1.16     yaml_2.3.10        
[29] pillar_1.9.0        jquerylib_0.1.4     MASS_7.3-61         classInt_0.4-10    
[33] cachem_1.1.0        Deriv_4.1.6         digest_0.6.37       stringi_1.8.4      
[37] sf_1.0-19           maketools_1.3.1     fastmap_1.2.0       grid_4.4.2         
[41] colorspace_2.1-1    cli_3.6.3           magrittr_2.0.3      utf8_1.2.4         
[45] e1071_1.7-16        scales_1.3.0        backports_1.5.0     Sim.DiffProc_4.9   
[49] signal_1.8-1        igraph_2.1.1        gridExtra_2.3       png_0.1-8          
[53] kableExtra_1.4.0    pbapply_1.7-2       evaluate_1.0.1.9000 dtw_1.23-1         
[57] fftw_1.0-9          testthat_3.2.1.1    rlang_1.1.4         Rcpp_1.0.13-1      
[61] glue_1.8.0          DBI_1.2.3           xml2_1.3.6          svglite_2.1.3      
[65] rstudioapi_0.17.1   jsonlite_1.8.9      R6_2.5.1            systemfonts_1.1.0  
[69] units_0.8-5