Difference between revisions of "Nyquist Analyze Plug-ins"

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Authors: Alex S. Brown and Steve Daulton
Authors: Alex S. Brown and Steve Daulton
{{intro|1=This is an updated and bug-fixed clone of the "Silence Finder" plug-in that was shipped with Audacity 2.x.|
{{intro|1=This is an updated and bug-fixed clone of the "Silence Finder" plug-in that was shipped with Audacity 2.x.|
2=Silence Finder looks for quiet parts ("silences") within the selected audio track and adds a point label at a specified distance before the end of each found "silent" region.}}
2=Silence Finder looks for quiet parts ("silences") within the selected audio track and adds a point label at a specified distance before the end of each detected "silent" region.}}

Revision as of 21:23, 7 June 2021

These are optional plug-in effects for Audacity. They are written in the Nyquist programming language. To install Nyquist plug-ins, see this page in the Manual.

"Analyze Plug-ins" appear in the Audacity Analyze menu. Plug-ins that output text or labels will usually be in this menu.

Unless otherwise indicated, these plug-ins are released under the terms of the GNU General Public License.
Related article(s):
Warning icon Feedback and bug reports:
  • All new plug-ins added to this list are tested in the Audacity version current at the time, but many of the older plug-ins are still in need of testing.
    • Please report any bugs to the Nyquist section of the Audacity forum so they may be fixed.
  • Please also let us know which plug-ins you like and find useful as that will help us to develop the types of plug-ins that users want.

Downloading and Installing Plug-ins

Please see the Download Nyquist Plug-ins page.

Analyze Plug-ins

ACX Check

(Acx-Check.ny) Download

Author: Steve Daulton

Based on a plug-in by Will McCown.

This analyzer was developed as an aid for audiobook producers. It displays a number of useful statistics about the selected audio, and compares them to the specifications published by ACX (an Amazon.com subsidiary).

Displayed Results:

Peak level: Maximum peak level in the selection
RMS level: The RMS level of the selected audio.
Noise floor: The RMS level of the quietest 500 milliseconds in the selection
Warnings: These are only displayed when applicable.
Warning: ACX require 44100 Hz sample rate.
Warning: ACX require running time no longer than 120 minutes
Noise floor: -inf dB Warning (too low - Dead silence sounds unnatural.) ACX require constant, low level "room tone" rather than an unnaturally silent background noise level.
Bulb icon The most common causes of the "Noise floor: ...dB Warning (too low - Dead silence sounds unnatural.)" message are:
  • Excessive use of Noise Reduction or Noise Gating.
  • Accidental inclusion of "absolute silence"

In either case, the Label Sounds effect may be used to find where the problem occurs.


  • This tool is intended only as an aid in achieving ACX acceptance. Even straight passes from this tool is NO guarantee of ACX acceptance.
  • The Noise Floor measurement is taken from the quietest half second of audio found in the selection. If one part of the selection is quieter than the rest, you will get a false value.
  • Minimum selection length is 1/2 second.
  • Maximum selection length is about 2.14 billion samples (13.5 hours at a sample rate of 44100 Hz)

Also beware that some noise sources are worse than others, and noise such as the 1000 Hz whine that often happens in USB audio interfaces may result in an ACX rejection even though it is below the -60 dBFS noise floor requirement.

See also: Audiobook Mastering.

Peak Finder rft

(Peakfinder-rft.ny) Download

Author: Edgar-rft.

Either places a single label at the first instance of a peak volume, or multiple labels at all the instances of that peak.


  1. Place labels at: [Choice: first peak only, all equally loud peaks (default)] The default setting will create labels for all peaks at the maximum absolute amplitude. "Absolute" amplitude disregards whether the value is positive or negative, so peaks may be up or down.
  2. Minimum Distance: [samples]: [1 to 1000, (default 100)] The minimum distance between labels (in samples). If audio is clipped there may be many samples in succession at the maximum amplitude. This setting avoids labeling every successive sample by setting a minimum distance between labels.


  • This effect can be very slow on long selections.
  • If the audio is clipped and "Place labels at: all equally loud peaks" is selected, there may be an extremely large number of labels created. The "Minimum Distance" setting is useful to reduce the number of labels.
  • Peaks that appear to be at the maximum amplitude will not be labeled unless they are exactly at the maximum amplitude.

Pitch Detect

(pitch-detect.ny) Download

Author: Steve Daulton

This plug-in attempts to detect and display the musical pitch and frequency of the selected note. In most cases the default settings will work best. The other options are provided to handle special cases such as analyzing synthetic signals that are outside of the usual musical range.

By default, the plug-in detects the pitch by analyzing the first 0.2 seconds of the selection. In most cases this should work well. If required the analyzed section can be set to the first part of the selection ranging from the first 10th of a second (0.1 seconds) up to one second.


  1. Frequency range: [Choice: 20-1000 Hz, 100-2000 Hz, 1 kHz-10 kHz. Default 100-2000 Hz] In most cases the default should be used as most musical pitches are in the range 100 to 2000 Hz.
  2. Analyse first (seconds): [0.1 to 1. Default 0.2] At the default setting the first 0.2 seconds of the selection will be analyzed.

Limitations: This plug-in is intended to detect single notes - you may get strange results if you try to analyze chords.

Extremely high frequencies may not be detected very accurately, especially if the sample rate is not very high. The plug-in will often detect very high frequencies better if the sample rate is 96000 Hz rather than 44100 Hz.

The plug-in should usually be able to detect pitches of single notes to within a few percent of the actual frequency. Don't expect the frequency in Hz to be exact..

Advanced usage tips:

  • For detecting very low frequencies (less than a few hundred Hz) the plug-in should be set to the low frequency range (20 to 1000 Hz).
  • For detecting very high frequencies (several kHz) the plug-in should be set to the high frequency range (1 kHz to 10 kHz).
  • For measuring synthesized tones and other electronic signals, the most accurate measure of frequency in Audacity is to use "Plot Spectrum" and set the "Size" setting to a high value.

Regular Interval Labels

(equalabl.ny) Download

Author: David R.Sky


  1. Label interval: [seconds]: Default sixty seconds between labels, from one second to six hundred seconds [ten minutes].
  2. Label text: The text that will appear in each label, default is "label".
  3. Prepend numbers to label text [0=no 1=yes]: Default is yes, so your labels would sequentially be "0label 1label..." and so on, using the default text.
  4. Final label: [0=exclude 1=include] Example; if your selection is sixty seconds long, and your label interval is ten seconds, the final label would be at the exact end of your selection. By default, the above variable is to exclude [not set] the final label.
  5. Final audio segment duration equal with others: [0=no 1=yes] Your label interval setting may result in the final segment of audio being unequal with the preceding ones. By default, the above variable is set to make the final audio segment equal in duration with the preceding ones. This might make the label interval slightly different from your chosen one, depending on the size of the final audio segment.

Users of screen readers: Labels may be viewed by opening the track menu [alt+t] and clicking on 'edit labels'. The labels and their time positions can be read by cursoring up and down and left-right. press alt+f4 to return to the main Audacity screen.

Released to the Audacity community June 25, 2007.

Thanks to:

  • Sami Jumppanen from the Audacity users group for suggesting this plug-in.
  • Leland Lucius from the Audacity development list for code feedback which helped wake me from late night programming! and thanks to Gale Andrews from the Audacity development list for suggesting improvements.
  • Alex S. Brown for example code from his silencemarker.ny plug-in for placing labels on the label track.

Selection Duration

(duration.ny) Download

Authors: David R.Sky, Steven Jones, Dominic Mazzoni

This plug-in gives the duration of audio you have selected, in either time units or samples as preferred. Current Audacity has a Selection Toolbar providing a screen-reader friendly display of selection start time and duration, but if you're using 1.2.x with a screen reader, this plug-in provides an easy solution. If you have opened or imported more than one track and have not yet done a Quick Mix, the duration of each track loaded into Audacity is given in the order it appears on the screen. Simply press ENTER after each track duration is given. The final screen gives information from Nyquist, which you can ignore. Simply press ENTER again to return to the regular Audacity screen.

Silence Finder

(SilenceFinder.ny) Download

Authors: Alex S. Brown and Steve Daulton

This is an updated and bug-fixed clone of the "Silence Finder" plug-in that was shipped with Audacity 2.x.
Silence Finder looks for quiet parts ("silences") within the selected audio track and adds a point label at a specified distance before the end of each detected "silent" region.


  • Treat audio below this level as silence [dB]: [-100 to 0 dB (default -26 dB)] Audio below this level is considered to be a "silence".
  • Minimum duration of silence [seconds]: [0.1 to 5.0 seconds (default 1.0 seconds)] Minimum length of silence that will have a label added. Gaps in the sound that are shorter than this are ignored.
  • Label placement [seconds before silence ends]: [0 to 1 seconds (default 0.3 second)] Each detected silence will have a label added at this distance before the sound level rises above the specified "silence level".

If the selected audio ends with a long enough period of silence, a final label is added at "Minimum duration of silence" after the final sound.

Usage Tips:

  1. If the plug-in appears to miss some some long gaps (not enough labels), try increasing the threshold level (the first control).
  2. If the plug-in appears to miss some shorter gaps that you want labeled, try reducing the minimum silence duration (the second control).
  3. If the plug-in adds labels to quiet parts that you don't want labeled, try lowering the threshold level, and / or increasing the minimum silence duration.
  4. If you require more control over the type of labels, or label placement, try the "Label Sounds" effect that is shipped with Audacity 3.x.