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+ + 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. +
+ ++ 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: +
++ 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 : +
++ 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 + below. +
+ ++ In the Note Onset mode, more parameters are active: +
+| Detection function | The method used to detect note changes. More on + this below. |
|---|---|
| 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 Jonathan 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. +
+ +
+ 
+ 
+ + 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
+ 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 then Selected Regions > Position > + Snap position to grid. +