synaudio-cli

A command line tool for aligning and synchronizing two or more audio clips based on their content.

Based on synaudio

How it works

synaudio-cli accepts two files, one base file and one comparison and writes out a copy of the comparison file that is aligned to the start and the speed of the base file.

• The first file supplied is the base. It is used as the basis of comparison.
• The second file supplied is the comparison. A copy of this file that is synchronized against the base will be saved to disk.
  • These two files supplied should have audio that is similar, but the audio does not need to be an exact match.
    • The less similar the audio data is, the less likely a successful match will happen.
  • Examples:
    • Two recordings of the same audio taken at different times or with different devices (analog or digital).
    • Two recordings of the same source, but taken with different microphones, or using a slightly different audio mix.
    • Two recordings of the same audio, one synced to a video, and another in a separate audio file that was not synced to the video.
    • Two recordings of an analog tape, one that is synced, but has noise or low fidelity, and another newer recording that is not synced by has higher fidelity.
    • Two digital recordings of the same audio, but the recordings don't match due to clock miss-match and/or clock drift.
• The comparison file is decoded into small comparison samples that are taken at regular intervals.
• Each comparison sample is then synchronized against the base using the Pearson correlation coefficient algorithm to determine where each comparison sample matches up in the base file.
  • See synaudio for details
• The difference between each comparison sample's calculated sample offset and actual sample offset is processed through a linear regression and used to synchronize the comparison file against the base
  • The comparison file is trimmed or padded at the beginning based on the linear regression intercept
  • The comparison file is rate adjusted based on the linear regression slope
  • (Optional) The comparison file is normalized, either as a whole, or as independent channels.

Example

The below visual example is a screenshot from an audio editor of the base, comparison, and final output synced files. This example was generated from two recordings from analog tape, one mono low fidelity recording (base) and another stereo high fidelity recording (comparison). The image is cut in the middle so the beginning and end of the audio are both visible.

$ synaudio-cli --normalize-independent base.ogg comparison.flac
Decoding files...
Synchronizing files... 100%
Trim start 15.36761384342938 Trim end 3530.78 Rate 0.9999550657881119
Adjusting offset and speed...
Normalizing each channel...
Encoding output file... comparison.synced.flac
Done

Installation

NPM

Pre-requisites

• Node.js JavaScript runtime
• sox, ffmpeg, flac audio processing tools
  • Ensure the sox, ffmpeg, ffprobe (part of ffmpeg), and flac executables are available in your PATH environment variable

Installing synaudio-cli

• From a terminal, run npm i -g synaudio-cli

Usage

$ synaudio-cli base.ogg comparison.flac

• Synchronizes comparison.flac to align with base.ogg

$ synaudio-cli --normalize-independent base.ogg comparison.flac

• Synchronizes comparison.flac to align with base.ogg, and normalizes each channel of the output file independently

Options

$ synaudio-cli --help
index.js <base-file> <comparison-file>

syncs the <comparison_file> to the <base_file>

Sync Options:
  -R, --rectify         Rectify the audio before comparing for better cross-correlation  [boolean] [default: true]
  -T, --rate-tolerance  Duration in seconds describing how much +- the rate might differ from the base file.  [number] [default: 0.5]
  -L, --sample-length   Duration in seconds of each comparison file sample.  [number] [default: 0.125]
  -G, --sample-gap      Duration in seconds to skip between samples of the comparison file.  [number] [default: 10]
  -S, --start-range     Duration in seconds to try to sync before the sample.  [number] [default: 180]
  -E, --end-range       Duration in seconds to try to sync after the sample.  [number] [default: 60]

Output Options:
  -d, --delete-comparison      Delete the original comparison file after successfully syncing.  [boolean] [default: false]
  -n, --normalize              Normalize the output audio.  [boolean] [default: false]
  -m, --normalize-independent  Normalize the output audio independently for each channel.  [boolean] [default: false]
  -e, --encode-options         Encode options supplied to `flac`  [string] [default: "--best"]
  -r, --rename-string          String to insert in the synced file before the extension. i.e. comparison.flac -> comparison.synced.flac  [string] [default: ".synced"]

Positionals:
  base-file        File used as the base of comparison.  [string]
  comparison-file  File that will be synced against the base file.  [string]

Options:
      --help          Show help  [boolean]
      --version       Show version number  [boolean]
  -t, --threads       Number of threads to spawn while comparing audio.  [number] [default: 16]
      --flac-threads  Number of threads to spawn while encoding using `flac`. Set to 1 to disable threading.  [number] [default: 16]