+ The Rhythm Ferret is a dedicated tool to speed up the usually labor intensive
+ task of slicing and adjusting a sound region to match a specific time grid. It is
+ especially useful for drum tracks, either to match a different tempo, or to
+ adjust a slightly out of tempo performance.
+
+
+ It is not limited to this use though, as it supports both percussive and note
+ type detection, and can be used on melodic material too.
+
+
Accessing the Rhythm Ferret
+
+
+ The Rhythm Ferret window can be accessed by Right clicking
+ any audio region, then Name_Of_The_Region > Edit
+ > Rhythm Ferret.
+
+
+ Once the window is open, selecting any region will make it the focus of the
+ Rhythm Ferret's detection, hence allowing to process multiple regions sequentially
+ without reopening the window each time.
+
+
+ The window itself is made of:
+
+
+
a "mode" selection
+
some parameters for this mode
+
an operation selection, that for now only allows to Split
+ regions.
+
+
+
+
The "Mode" selection
+
+
+ As the Rhythm Ferret is able to detect both percussive hits and melodic notes,
+ it is important to choose the best suited mode for the considered material,
+ so that Ardour can perform the detection with the greatest accuracy :
+
+
+
Percussive Onset will detect the start of each hit based
+ on the sudden change in energy (= volume) of the waveform
+
Note Onset will detect the start of each note based on the changes
+ in the frequency domain.
+
+
+
+
+
The Percussive Onset mode
+
+
+ In this mode, only two parameters are active:
+
+
+
Sensitivity (%)
The proportion of the samples that must exceed the
+ energy rise threshold in order for an onset to be detected (at frames in which
+ the detection function peaks). This roughly corresponds to how "noisy" a percussive
+ sound must be in order to be detected.
+
Cut Pos Threshold (dB)
The rise in energy amongst a group of samples
+ that is required for that to be counted toward the detection function's count.
+ This roughly corresponds to how "loud" a percussive sound must be in order to
+ be detected.
+
+
+ As those parameters are very material-related, there is no recipe for a perfect
+ match, and a good peak detection is a matter of adjusting those two parameters
+ by trial and error, and trying using the Analyze button
+ after each try.
+
+
+ Vertical grey markers will appear on the selected region, showing where Ardour
+ detects onsets as per the parameters. This markers can be manually adjusted, see
+ bellow.
+
+
+
The Note Onset Mode
+
+
+ In the Note Onset mode, more parameters are active:
+
+
+
Detection function
The method used to detect note changes. More on
+ this bellow.
+
Trigger gap (postproc) (ms)
Set the minimum inter-onset interval,
+ in milliseconds, i.e. the shortest interval between two consecutive onsets.
+
+
Peak threshold
Set the threshold value for the onset peak picking.
+ Lower threshold values imply more onsets detected. Increasing this threshold
+ should reduce the number of incorrect detections.
+
Silence threshold (dB)
Set the silence threshold, in dB, under which
+ the onset will not be detected. A value of -20.0 would eliminate most onsets
+ but the loudest ones. A value of -90.0 would select all onsets.
+
+
+
+ The Detection function, used in Note Onset mode to choose the mathematical strategy
+ used to detect the note changes, is user-selectable:
+
+
+
Energy based
This function calculates the local energy of the input
+ spectral frame
+
Spectral Difference
Spectral difference onset detection function
+ based on Jonhatan Foote and Shingo Uchihashi's "The beat spectrum: a new
+ approach to rhythm analysis" (2001)
+
High-Frequency Content
This method computes the High Frequency
+ Content (HFC) of the input spectral frame. The resulting function is efficient
+ at detecting percussive onsets. Based on Paul Masri's "Computer modeling
+ of Sound for Transformation and Synthesis of Musical Signal" (1996)
+
Complex Domain
This function uses information both in frequency and
+ in phase to determine changes in the spectral content that might correspond
+ to musical onsets. It is best suited for complex signals such as polyphonic
+ recordings.
+
Phase Deviation
This function uses information both energy and in
+ phase to determine musical onsets.
+
Kullback-Liebler
Kulback-Liebler onset detection function based on
+ Stephen Hainsworth and Malcom Macleod's "Onset detection in music audio
+ signals" (2003)
+
Modified Kullback-Liebler
Modified Kulback-Liebler onset detection
+ function based on Paul Brossier's "Automatic annotation of musical audio for
+ interactive systems" (2006)
+
+
+
+ Ardour defaults to Complex Domain, which usually gives good result for harmonic
+ material.
+
+
+
Manual adjustment
+
+
+
+
+
+
+ The Rhythm Ferret: Analyzing, Splitting regions, and snapping to grid
+
+
+
+
+ Using the Rhythm Ferret consists usually in finding the right parameters to
+ split the audio, by adjusting them and clicking the
+ Analyze button. Each time an analysis is run, Ardour
+ erases the previous results, and creates grey markers on the region according
+ to the parameters. Those markers can be manually dragged with the
+ LEFT mouse button to adjust their positions.
+
+
+ Once the markers are suitably placed, the second button in the down hand side
+ of the Rhythm Ferret window allows to Apply the operation.
+ At the moment of writing, only the Split Region is
+ available, which will split the region at the markers.
+
+
+ Those regions can then be manually aligned, or have their sync points set to
+ the closest grid (as per the Grid settings in
+ effect), by selecting all the regions, and using the
+ RIGHT click > Selected Regions > Position >
+ Snap position to grid.
+
+ 
+ 
+ 
+