diff --git a/DESCRIPTION b/DESCRIPTION
index a2e8600..6ea7ea5 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,6 +1,6 @@
 Package: hrep
 Title: Harmony Representations
-Version: 0.16.1
+Version: 0.20.0
 Authors@R: person("Peter", "Harrison", email = "pmc.harrison@gmail.com", role = c("aut", "cre"))
 Description: This package provides utilities for representing and manipulating 
     chord sequences for perceptually informed harmony modelling.
@@ -18,7 +18,7 @@ Suggests:
     testthat (>= 2.1.0),
     covr (>= 3.2.0),
     ggplot2 (>= 3.0.0)
-RoxygenNote: 7.2.3
+RoxygenNote: 7.3.1
 Imports: 
     plyr (>= 1.8.4),
     Rdpack (>= 0.9.0),
diff --git a/NEWS.md b/NEWS.md
index 4379f60..acc8493 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,3 +1,11 @@
+# hrep 0.20.0
+
+# hrep 0.19.0
+
+# hrep 0.18.0
+
+# hrep 0.17.0
+
 # hrep 0.16.1
 
 - Remove unnecessary info messages.
diff --git a/R/expand-harmonics.R b/R/expand-harmonics.R
index 57b2bde..216a753 100644
--- a/R/expand-harmonics.R
+++ b/R/expand-harmonics.R
@@ -13,7 +13,7 @@
 #' Number of harmonics (including the fundamental) to which
 #' each tone should be expanded.
 #'
-#' @param roll_off (Numeric scalar) Parametrises the amount of amplitude roll-off
+#' @param roll_off_dB (Numeric scalar) Parametrises the amount of amplitude roll-off
 #' in the harmonics, with greater values corresponding to higher roll-off.
 #'
 #' @param digits
@@ -22,16 +22,20 @@
 #' @param label_harmonics
 #' If TRUE, then the harmonics in the resulting spectrum are labelled with their harmonic numbers.
 #'
+#' @param pseudo_octave
+#' The octave ratio for stretching and compressing harmonics, defaults to 2.0.
+#'
 #' @rdname expand_harmonics
 #'
 #' @inheritParams collapse_summing_amplitudes
 #' @export
 expand_harmonics <- function(x,
                              num_harmonics = 11L,
-                             roll_off = 1,
+                             roll_off_dB = 1,
                              digits = 6,
                              label_harmonics = FALSE,
-                             coherent = FALSE) {
+                             coherent = FALSE,
+                             pseudo_octave = 2.0) {
   UseMethod("expand_harmonics")
 }
 
@@ -39,13 +43,14 @@ expand_harmonics <- function(x,
 #' @export
 expand_harmonics.sparse_fr_spectrum <- function(x,
                                                 num_harmonics = 11L,
-                                                roll_off = 1,
+                                                roll_off_dB = 1,
                                                 digits = 6,
                                                 label_harmonics = FALSE,
-                                                coherent = FALSE) {
+                                                coherent = FALSE,
+                                                pseudo_octave = 2.0) {
   expand_harmonics(sparse_pi_spectrum(x),
                    num_harmonics = num_harmonics,
-                   roll_off = roll_off,
+                   roll_off_dB = roll_off_dB,
                    digits = digits,
                    label_harmonics = label_harmonics,
                    coherent = coherent) %>%
@@ -56,18 +61,20 @@ expand_harmonics.sparse_fr_spectrum <- function(x,
 #' @export
 expand_harmonics.sparse_pi_spectrum <- function(x,
                                                 num_harmonics = 11L,
-                                                roll_off = 1,
+                                                roll_off_dB = 1,
                                                 digits = 6,
                                                 label_harmonics = FALSE,
-                                                coherent = FALSE) {
-  template <- pi_harmonic_template(num_harmonics, roll_off)
+                                                coherent = FALSE,
+                                                pseudo_octave = 2.0) {
   purrr::map2(pitch(x), amp(x),
               function(pitch, amp) {
+                n  <- seq_len(num_harmonics)
+                f0 <- midi_to_freq(pitch)
                 df <- data.frame(
-                  x = pitch + template$interval,
-                  y = amp * template$amplitude
+                  x = freq_to_midi(f0 * pseudo_octave ^ log2(n)),
+                  y = 1 * 10 ^ ( -roll_off_dB * log2(n) / 20)
                 )
-                if (label_harmonics) df$labels <- seq_along(template$interval)
+                if (label_harmonics) df$labels <- seq_along(df$x)
                 df
               }) %>%
     collapse_summing_amplitudes(digits = digits, coherent = coherent) %>%
@@ -78,19 +85,14 @@ expand_harmonics.sparse_pi_spectrum <- function(x,
 #' @export
 expand_harmonics.pi_chord <- function(x,
                                       num_harmonics = 11L,
-                                      roll_off = 1,
+                                      roll_off_dB = 1,
                                       digits = 6,
                                       label_harmonics = FALSE,
-                                      coherent = FALSE) {
+                                      coherent = FALSE,
+                                      pseudo_octave = 2.0) {
   sparse_pi_spectrum(x,
                      num_harmonics = num_harmonics,
-                     roll_off = roll_off,
+                     roll_off_dB = roll_off_dB,
                      digits = digits,
                      label_harmonics = label_harmonics)
 }
-
-pi_harmonic_template <- function(num_harmonics, roll_off, digits = 6) {
-  tibble::tibble(n = seq_len(num_harmonics),
-                 interval = 12 * log(.data$n, base = 2),
-                 amplitude = 1 / (.data$n ^ roll_off))
-}
diff --git a/R/smooth-pc-spectrum.R b/R/smooth-pc-spectrum.R
index 6e90dfe..1ca245f 100644
--- a/R/smooth-pc-spectrum.R
+++ b/R/smooth-pc-spectrum.R
@@ -75,7 +75,7 @@ smooth_pc_spectrum <- function(
   ...,
   sigma = 6.83,
   num_harmonics = 11L,
-  roll_off = 1,
+  roll_off_dB = 1,
   coherent = FALSE
 ) {
   UseMethod("smooth_pc_spectrum")
@@ -88,12 +88,12 @@ smooth_pc_spectrum.default <- function(
   ...,
   sigma = 6.83,
   num_harmonics = 11L,
-  roll_off = 1,
+  roll_off_dB = 1,
   coherent = FALSE
 ) {
   smooth_pc_spectrum(sparse_pc_spectrum(x,
                                         num_harmonics = num_harmonics,
-                                        roll_off = roll_off,
+                                        roll_off_dB = roll_off_dB,
                                         coherent = coherent),
                      sigma = sigma,
                      coherent = coherent,
diff --git a/R/smooth-pi-spectrum.R b/R/smooth-pi-spectrum.R
index 8133cbc..739c8f5 100644
--- a/R/smooth-pi-spectrum.R
+++ b/R/smooth-pi-spectrum.R
@@ -79,12 +79,12 @@ smooth_pi_spectrum <- function(x, sigma = 6.83, ...) {
 smooth_pi_spectrum.default <- function(x,
                                        sigma = 6.83,
                                        num_harmonics = 11L,
-                                       roll_off = 1,
+                                       roll_off_dB = 1,
                                        coherent = FALSE,
                                        ...) {
   smooth_pi_spectrum(sparse_pi_spectrum(x,
                                         num_harmonics = num_harmonics,
-                                        roll_off = roll_off,
+                                        roll_off_dB = roll_off_dB,
                                         coherent = coherent,
                                         ...),
                      sigma = sigma,
diff --git a/R/sparse-spectrum.R b/R/sparse-spectrum.R
index 253934f..df03599 100644
--- a/R/sparse-spectrum.R
+++ b/R/sparse-spectrum.R
@@ -78,14 +78,24 @@ set_labels.sparse_spectrum <- function(x, labels) {
 }
 
 #' @export
-plot.sparse_spectrum <- function(x, ggplot = FALSE, xlim = NULL, ...) {
+plot.sparse_spectrum <- function(x, cochlea=FALSE, ggplot = FALSE, xlim = NULL,
+                                 trans='identity', ...) {
   df <- as.data.frame(x)
+  if (cochlea) {
+    greenwood <- function(frequency) {
+      100 * (1 - (log10( frequency / 165.4 + 0.88 ) / 2.1))
+    }
+    df$x = greenwood(df$x)
+    x_label = 'Cochlea (%)'
+  } else {
+    x_label = x_lab(x)
+  }
   if (ggplot) {
     assert_installed("ggplot2")
       ggplot2::ggplot(df, ggplot2::aes_string(x = "x", xend = "x",
                                               y = 0, yend = "y")) +
       ggplot2::geom_segment() +
-      ggplot2::scale_x_continuous(x_lab(x), limits = xlim) +
+      ggplot2::scale_x_continuous(x_label, limits = xlim, transform=trans) +
       ggplot2::scale_y_continuous(y_lab(x))
   } else {
     n <- nrow(df)
@@ -95,7 +105,7 @@ plot.sparse_spectrum <- function(x, ggplot = FALSE, xlim = NULL, ...) {
       df2$x[I + 1:3] <- df$x[i]
       df2$y[I + 2L] <- df$y[i]
     }
-    plot(df2$x, df2$y, xlab = x_lab(x), ylab = y_lab(x),
+    plot(df2$x, df2$y, xlab = x_label, ylab = y_lab(x),
          type = "l", xlim = xlim, ...)
     if (!is.null(df$labels)) {
       for (i in seq_len(nrow(df))) {
diff --git a/man/expand_harmonics.Rd b/man/expand_harmonics.Rd
index 11aa277..623da60 100644
--- a/man/expand_harmonics.Rd
+++ b/man/expand_harmonics.Rd
@@ -10,37 +10,41 @@
 expand_harmonics(
   x,
   num_harmonics = 11L,
-  roll_off = 1,
+  roll_off_dB = 1,
   digits = 6,
   label_harmonics = FALSE,
-  coherent = FALSE
+  coherent = FALSE,
+  pseudo_octave = 2
 )
 
 \method{expand_harmonics}{sparse_fr_spectrum}(
   x,
   num_harmonics = 11L,
-  roll_off = 1,
+  roll_off_dB = 1,
   digits = 6,
   label_harmonics = FALSE,
-  coherent = FALSE
+  coherent = FALSE,
+  pseudo_octave = 2
 )
 
 \method{expand_harmonics}{sparse_pi_spectrum}(
   x,
   num_harmonics = 11L,
-  roll_off = 1,
+  roll_off_dB = 1,
   digits = 6,
   label_harmonics = FALSE,
-  coherent = FALSE
+  coherent = FALSE,
+  pseudo_octave = 2
 )
 
 \method{expand_harmonics}{pi_chord}(
   x,
   num_harmonics = 11L,
-  roll_off = 1,
+  roll_off_dB = 1,
   digits = 6,
   label_harmonics = FALSE,
-  coherent = FALSE
+  coherent = FALSE,
+  pseudo_octave = 2
 )
 }
 \arguments{
@@ -54,7 +58,7 @@ Should be of class
 Number of harmonics (including the fundamental) to which
 each tone should be expanded.}
 
-\item{roll_off}{(Numeric scalar) Parametrises the amount of amplitude roll-off
+\item{roll_off_dB}{(Numeric scalar) Parametrises the amount of amplitude roll-off
 in the harmonics, with greater values corresponding to higher roll-off.}
 
 \item{digits}{Number of digits to which each partial's MIDI pitch should be rounded.}
@@ -66,6 +70,8 @@ assuming coherent summation, where the amplitudes simply add together
 (default is \code{FALSE}).
 Otherwise incoherent summation is used, where the amplitudes are squared, added, then
 square rooted.}
+
+\item{pseudo_octave}{The octave ratio for stretching and compressing harmonics, defaults to 2.0.}
 }
 \description{
 Expands each tone in an object into its implied harmonics.
diff --git a/man/play_wav.Rd b/man/play_wav.Rd
index 783c0e7..0c4f4f1 100644
--- a/man/play_wav.Rd
+++ b/man/play_wav.Rd
@@ -33,10 +33,11 @@ Chord fade-out time (seconds).}
     \item{\code{num_harmonics}}{(Integerish scalar)
 Number of harmonics (including the fundamental) to which
 each tone should be expanded.}
-    \item{\code{roll_off}}{(Numeric scalar) Parametrises the amount of amplitude roll-off
+    \item{\code{roll_off_dB}}{(Numeric scalar) Parametrises the amount of amplitude roll-off
 in the harmonics, with greater values corresponding to higher roll-off.}
     \item{\code{digits}}{Number of digits to which each partial's MIDI pitch should be rounded.}
     \item{\code{label_harmonics}}{If TRUE, then the harmonics in the resulting spectrum are labelled with their harmonic numbers.}
+    \item{\code{pseudo_octave}}{The octave ratio for stretching and compressing harmonics, defaults to 2.0.}
     \item{\code{coherent}}{Whether the amplitudes from different spectral components should be combined
 assuming coherent summation, where the amplitudes simply add together
 (default is \code{FALSE}).
diff --git a/man/save_wav.Rd b/man/save_wav.Rd
index a990c0e..c9b6fa4 100644
--- a/man/save_wav.Rd
+++ b/man/save_wav.Rd
@@ -47,10 +47,11 @@ used to avoid clicks and other artifacts.}
     \item{\code{num_harmonics}}{(Integerish scalar)
 Number of harmonics (including the fundamental) to which
 each tone should be expanded.}
-    \item{\code{roll_off}}{(Numeric scalar) Parametrises the amount of amplitude roll-off
+    \item{\code{roll_off_dB}}{(Numeric scalar) Parametrises the amount of amplitude roll-off
 in the harmonics, with greater values corresponding to higher roll-off.}
     \item{\code{digits}}{Number of digits to which each partial's MIDI pitch should be rounded.}
     \item{\code{label_harmonics}}{If TRUE, then the harmonics in the resulting spectrum are labelled with their harmonic numbers.}
+    \item{\code{pseudo_octave}}{The octave ratio for stretching and compressing harmonics, defaults to 2.0.}
     \item{\code{coherent}}{Whether the amplitudes from different spectral components should be combined
 assuming coherent summation, where the amplitudes simply add together
 (default is \code{FALSE}).
diff --git a/man/smooth_pc_spectrum.Rd b/man/smooth_pc_spectrum.Rd
index 570d246..035021e 100644
--- a/man/smooth_pc_spectrum.Rd
+++ b/man/smooth_pc_spectrum.Rd
@@ -11,7 +11,7 @@ smooth_pc_spectrum(
   ...,
   sigma = 6.83,
   num_harmonics = 11L,
-  roll_off = 1,
+  roll_off_dB = 1,
   coherent = FALSE
 )
 
@@ -20,7 +20,7 @@ smooth_pc_spectrum(
   ...,
   sigma = 6.83,
   num_harmonics = 11L,
-  roll_off = 1,
+  roll_off_dB = 1,
   coherent = FALSE
 )
 
@@ -41,7 +41,7 @@ perceptual blurring. Defaults to 6.83 cents, after
 Number of harmonics (including the fundamental) to which
 each tone should be expanded.}
 
-\item{roll_off}{(Numeric scalar) Parametrises the amount of amplitude roll-off
+\item{roll_off_dB}{(Numeric scalar) Parametrises the amount of amplitude roll-off
 in the harmonics, with greater values corresponding to higher roll-off.}
 
 \item{coherent}{Whether the amplitudes from different spectral components should be combined
diff --git a/man/smooth_pi_spectrum.Rd b/man/smooth_pi_spectrum.Rd
index 2cb8295..6d691ae 100644
--- a/man/smooth_pi_spectrum.Rd
+++ b/man/smooth_pi_spectrum.Rd
@@ -12,7 +12,7 @@ smooth_pi_spectrum(x, sigma = 6.83, ...)
   x,
   sigma = 6.83,
   num_harmonics = 11L,
-  roll_off = 1,
+  roll_off_dB = 1,
   coherent = FALSE,
   ...
 )
@@ -34,7 +34,7 @@ perceptual blurring. Defaults to 6.83 cents, after
 Number of harmonics (including the fundamental) to which
 each tone should be expanded.}
 
-\item{roll_off}{(Numeric scalar) Parametrises the amount of amplitude roll-off
+\item{roll_off_dB}{(Numeric scalar) Parametrises the amount of amplitude roll-off
 in the harmonics, with greater values corresponding to higher roll-off.}
 
 \item{coherent}{Whether the amplitudes from different spectral components should be combined
diff --git a/man/sparse_fr_spectrum.Rd b/man/sparse_fr_spectrum.Rd
index a9732bd..e524f0e 100644
--- a/man/sparse_fr_spectrum.Rd
+++ b/man/sparse_fr_spectrum.Rd
@@ -39,10 +39,11 @@ and correspond to a numeric vector of amplitudes.
     \item{\code{num_harmonics}}{(Integerish scalar)
 Number of harmonics (including the fundamental) to which
 each tone should be expanded.}
-    \item{\code{roll_off}}{(Numeric scalar) Parametrises the amount of amplitude roll-off
+    \item{\code{roll_off_dB}}{(Numeric scalar) Parametrises the amount of amplitude roll-off
 in the harmonics, with greater values corresponding to higher roll-off.}
     \item{\code{digits}}{Number of digits to which each partial's MIDI pitch should be rounded.}
     \item{\code{label_harmonics}}{If TRUE, then the harmonics in the resulting spectrum are labelled with their harmonic numbers.}
+    \item{\code{pseudo_octave}}{The octave ratio for stretching and compressing harmonics, defaults to 2.0.}
     \item{\code{coherent}}{Whether the amplitudes from different spectral components should be combined
 assuming coherent summation, where the amplitudes simply add together
 (default is \code{FALSE}).
diff --git a/man/sparse_pc_spectrum.Rd b/man/sparse_pc_spectrum.Rd
index 3d6b13c..de6040d 100644
--- a/man/sparse_pc_spectrum.Rd
+++ b/man/sparse_pc_spectrum.Rd
@@ -27,10 +27,11 @@ sparse_pc_spectrum(x, ...)
     \item{\code{num_harmonics}}{(Integerish scalar)
 Number of harmonics (including the fundamental) to which
 each tone should be expanded.}
-    \item{\code{roll_off}}{(Numeric scalar) Parametrises the amount of amplitude roll-off
+    \item{\code{roll_off_dB}}{(Numeric scalar) Parametrises the amount of amplitude roll-off
 in the harmonics, with greater values corresponding to higher roll-off.}
     \item{\code{digits}}{Number of digits to which each partial's MIDI pitch should be rounded.}
     \item{\code{label_harmonics}}{If TRUE, then the harmonics in the resulting spectrum are labelled with their harmonic numbers.}
+    \item{\code{pseudo_octave}}{The octave ratio for stretching and compressing harmonics, defaults to 2.0.}
   }}
 
 \item{coherent}{Whether the amplitudes from different spectral components should be combined
diff --git a/man/sparse_pi_spectrum.Rd b/man/sparse_pi_spectrum.Rd
index 0c230bf..40dd482 100644
--- a/man/sparse_pi_spectrum.Rd
+++ b/man/sparse_pi_spectrum.Rd
@@ -30,10 +30,11 @@ sparse_pi_spectrum(x, ...)
     \item{\code{num_harmonics}}{(Integerish scalar)
 Number of harmonics (including the fundamental) to which
 each tone should be expanded.}
-    \item{\code{roll_off}}{(Numeric scalar) Parametrises the amount of amplitude roll-off
+    \item{\code{roll_off_dB}}{(Numeric scalar) Parametrises the amount of amplitude roll-off
 in the harmonics, with greater values corresponding to higher roll-off.}
     \item{\code{digits}}{Number of digits to which each partial's MIDI pitch should be rounded.}
     \item{\code{label_harmonics}}{If TRUE, then the harmonics in the resulting spectrum are labelled with their harmonic numbers.}
+    \item{\code{pseudo_octave}}{The octave ratio for stretching and compressing harmonics, defaults to 2.0.}
   }}
 
 \item{amplitude}{(Numeric vector)
diff --git a/man/wave.Rd b/man/wave.Rd
index 0cf9c4c..93dd88b 100644
--- a/man/wave.Rd
+++ b/man/wave.Rd
@@ -36,10 +36,11 @@ wave(x, ...)
     \item{\code{num_harmonics}}{(Integerish scalar)
 Number of harmonics (including the fundamental) to which
 each tone should be expanded.}
-    \item{\code{roll_off}}{(Numeric scalar) Parametrises the amount of amplitude roll-off
+    \item{\code{roll_off_dB}}{(Numeric scalar) Parametrises the amount of amplitude roll-off
 in the harmonics, with greater values corresponding to higher roll-off.}
     \item{\code{digits}}{Number of digits to which each partial's MIDI pitch should be rounded.}
     \item{\code{label_harmonics}}{If TRUE, then the harmonics in the resulting spectrum are labelled with their harmonic numbers.}
+    \item{\code{pseudo_octave}}{The octave ratio for stretching and compressing harmonics, defaults to 2.0.}
     \item{\code{coherent}}{Whether the amplitudes from different spectral components should be combined
 assuming coherent summation, where the amplitudes simply add together
 (default is \code{FALSE}).
diff --git a/tests/testthat/test-expand_harmonics.R b/tests/testthat/test-expand_harmonics.R
index 2023abb..1491aa3 100644
--- a/tests/testthat/test-expand_harmonics.R
+++ b/tests/testthat/test-expand_harmonics.R
@@ -36,14 +36,14 @@ test_that("misc", {
 
 test_that("roll-off", {
   pi_chord(0) %>%
-    expand_harmonics(num_harmonics = 6, roll_off = 2) %>%
+    expand_harmonics(num_harmonics = 6, roll_off_dB = 2) %>%
     {amp(.)} %>%
     expect_equal(c(1, 1 / 2 ^ 2, 1 / 3 ^ 2, 1 / 4 ^ 2, 1 / 5 ^ 2, 1 / 6 ^ 2))
 })
 
 test_that("MIDI transposition", {
   pi_chord(0) %>%
-    expand_harmonics(num_harmonics = 6, roll_off = 2) %>%
+    expand_harmonics(num_harmonics = 6, roll_off_dB = 2) %>%
     {pitch(.)} %>%
     expect_equal(c(10, 22, 29, 34, 38, 41),
                  tolerance = 1)
@@ -79,3 +79,43 @@ test_that("rounding", {
     c(0, 7) %>% sparse_pi_spectrum(digits = 0)
   )
 })
+test_that('octave ratio stretches and compresses',{
+  harmonic_default_result <- 60 %>%
+    sparse_pi_spectrum(num_harmonics=10) %>%
+    pitch
+  expect_equal(harmonic_default_result[1], 60)
+  expect_equal(harmonic_default_result[2], 60+12)
+  expect_equal(harmonic_default_result[4], 60+24)
+  expect_equal(harmonic_default_result[8], 60+36)
+
+  harmonic_explicit_result <- 60 %>%
+    sparse_pi_spectrum(num_harmonics=10, pseudo_octave = 2.0) %>%
+    pitch
+  expect_equal(harmonic_explicit_result[1], 60)
+  expect_equal(harmonic_explicit_result[2], 60+12)
+  expect_equal(harmonic_explicit_result[4], 60+24)
+  expect_equal(harmonic_explicit_result[8], 60+36)
+
+  compressed_result <- 60 %>%
+    sparse_pi_spectrum(num_harmonics=10, pseudo_octave = 1.9) %>%
+    pitch
+  expect_equal(compressed_result[1], 60)
+  expect_equal(compressed_result[2],
+               freq_to_midi(midi_to_freq(60)*1.9^log2(2)))
+  expect_equal(compressed_result[4],
+               freq_to_midi(midi_to_freq(60)*1.9^log2(4)))
+  expect_equal(compressed_result[8],
+               freq_to_midi(midi_to_freq(60)*1.9^log2(8)))
+
+  stretcheded_result <- 60 %>%
+    sparse_pi_spectrum(num_harmonics=10, pseudo_octave = 2.1) %>%
+    pitch
+  expect_equal(stretcheded_result[1], 60)
+  expect_equal(stretcheded_result[2],
+               freq_to_midi(midi_to_freq(60)*2.1^log2(2)))
+  expect_equal(stretcheded_result[4],
+               freq_to_midi(midi_to_freq(60)*2.1^log2(4)))
+  expect_equal(stretcheded_result[8],
+               freq_to_midi(midi_to_freq(60)*2.1^log2(8)))
+
+})
diff --git a/tests/testthat/test-gaussian_filter.R b/tests/testthat/test-gaussian_filter.R
index 6d16e1d..89599e0 100644
--- a/tests/testthat/test-gaussian_filter.R
+++ b/tests/testthat/test-gaussian_filter.R
@@ -4,7 +4,7 @@ test_that("worked example", {
   fr_chord(100) %>%
     filter_spectrum_gaussian(location = c(100, 1000, 2000),
                              width = 100,
-                             roll_off = 0, num_harmonics = 30) %>%
+                             roll_off_dB = 0, num_harmonics = 30) %>%
     tibble::as_tibble() %>%
     (function(x) x[x$y > 0.2, ]) %>%
     expect_equal(tibble::tribble(
diff --git a/tests/testthat/test-sparse_fr_spectrum.R b/tests/testthat/test-sparse_fr_spectrum.R
new file mode 100644
index 0000000..b7654d0
--- /dev/null
+++ b/tests/testthat/test-sparse_fr_spectrum.R
@@ -0,0 +1,42 @@
+context("test-sparse_fr_spectrum")
+
+test_that('octave ratio stretches and compresses',{
+  harmonic_default_result <- 60 %>%
+    sparse_fr_spectrum(num_harmonics=10) %>%
+    freq %>% freq_to_midi
+  expect_equal(harmonic_default_result[1], 60)
+  expect_equal(harmonic_default_result[2], 60+12)
+  expect_equal(harmonic_default_result[4], 60+24)
+  expect_equal(harmonic_default_result[8], 60+36)
+
+  harmonic_explicit_result <- 60 %>%
+    sparse_fr_spectrum(num_harmonics=10, pseudo_octave = 2.0) %>%
+    freq %>% freq_to_midi
+  expect_equal(harmonic_explicit_result[1], 60)
+  expect_equal(harmonic_explicit_result[2], 60+12)
+  expect_equal(harmonic_explicit_result[4], 60+24)
+  expect_equal(harmonic_explicit_result[8], 60+36)
+
+  compressed_result <- 60 %>%
+    sparse_fr_spectrum(num_harmonics=10, pseudo_octave = 1.9) %>%
+    freq %>% freq_to_midi
+  expect_equal(compressed_result[1], 60)
+  expect_equal(compressed_result[2],
+               freq_to_midi(midi_to_freq(60)*1.9^log2(2)))
+  expect_equal(compressed_result[4],
+               freq_to_midi(midi_to_freq(60)*1.9^log2(4)))
+  expect_equal(compressed_result[8],
+               freq_to_midi(midi_to_freq(60)*1.9^log2(8)))
+
+  stretcheded_result <- 60 %>%
+    sparse_fr_spectrum(num_harmonics=10, pseudo_octave = 2.1) %>%
+    freq %>% freq_to_midi
+  expect_equal(stretcheded_result[1], 60)
+  expect_equal(stretcheded_result[2],
+               freq_to_midi(midi_to_freq(60)*2.1^log2(2)))
+  expect_equal(stretcheded_result[4],
+               freq_to_midi(midi_to_freq(60)*2.1^log2(4)))
+  expect_equal(stretcheded_result[8],
+               freq_to_midi(midi_to_freq(60)*2.1^log2(8)))
+
+})