Audiotools

by Andrew Fish & Scot McSweeney-Roberts

Overview

If you've ever tried to create audio cd's from your tapes and lp's you have probably found that it can be a very time-consuming task which requires vast amounts of spare hard-drive space and a lot of patience. First you have to record your sample to hard-disk with a package which can handle huge samples and then you have to load it into your editor, trim the silences from the front and back, possibly cut it into tracks and save it as one or more files to your hard-disk before deleting your temporary file. Only then can you put your audio onto CD. What you should be able to do is run one program which does the whole thing.

Audiotools is a step in the right direction - whilst it can't write CD-R's, it can automate the rest of the process of recording audio, reducing noise levels, removing extraneous silences and dividing it up into tracks.

Basic Concept

The audio to the right of the yellow line is our signal, to the left is what we regard as silence. As can be seen, even in the silent area there is some noise either side of the zero dB line (the blue line). The maximum and minimum values of this noise (in absolute sample values) are known as the "noise floor". Due to the nature of samples, the signal spends some of its time below the noise floor, but this is for a limited period of time. Similarly "clicks" and "pops" may take the silence above the noise floor for limited periods. If we specify a minimum period of time below the noise floor to regard as a silence and a minimum time above it to regard as a signal, we can break audio into separate tracks or samples.

Audiotools interface

The Main Dialog

When you run the program you are presented with a dialog which has the following controls:

METHOD

Selects one of the three recording methods:

"Straight Record" Just record from the source to a file

"Top 'n' Tail" Record from the source, removing silence from the beginning and end of the recording. A silence of 20 seconds is automatically interpreted as the end of the recording, otherwise recording ends when you tell it to stop.

"Auto Tracking" This creates a series of numbered files which are all individually "topped 'n' tailed". A period of silence specified on the format dialog tells the algorithm when to start a new track.

SOURCE

Selects one of:

"File"

All methods can be applied to a file, although currently "Straight Record" has no real meaning with files. Working from file to file is faster than working from a soundcard, but requires that the file has been recorded already.

"Soundcard"

Performs methods on the system's default soundcard (See Windows 95 help on how to set this up)

RECORD

Starts recording from the specified input, using the specified method to the specified destination file(s).

PLAY

Plays the specified source file.

STOP

Stops playing or recording.

TRACK

When working from the soundcard in "Straight Record" or "Top 'n' Tail" modes, this allows you to manually break your recording into tracks. This is useful for live recordings where there isn't necessarily a silence between songs.

CLOSE

Exits the program

SOURCE FILE...

Selects a file for input both for file methods and for playback. This also sets the SOURCE to "File" to save time.

DESTINATION FILE...

Selects a file for output. When creating a series of files, the first will have the chosen name and subsequent files will have numbers from 1 upward appended (e.g. FRED.WAV, FRED1.WAV FRED2.WAV...).

Both SOURCE FILE and DESTINATION FILE have green led's beside them. These light when a file has been selected to let the user know which files have been selected.

FORMAT

Opens the format dialog (see below).

ABOUT

Shows information about the current version.

CLOSE

Closes the application

The Format Dialog

The format dialog configures the recording process and allows you to set parameters for the auto-tracking / top 'n' tailing operations.

FORMAT

Choose from 22KHz or 44KHz, Mono or Stereo

NOISE FLOOR LEVELS

This controls the noise-floor used in silence detection, usually you will use the "Analyse File" and "Analyse i/p" functions to set these, but you can set them manually.

MINIMUM SIL

The minimum length of time to be regarded as silence in milliseconds.

MINIMUM SIG

The minimum length of time to be regarded as a signal in milliseconds.

ANALYSE FILE

Allows you to select a file which is interpreted as silence. This is used to gather nosie-floor levels and initial noise reduction data.

ANALYSE I/P

Allows you to analyse a silent portion of your tape or lp. This is used to gather noise-floor levels and initial noise reduction data. With tape it is recommended that you analyse silence beyond the lead-in in order to get accurate figures.

AUTO-TRACK INITIAL SEQUENCE NUMBER

Tracks generated by auto-track are derived from a basic filename (such as file.wav) with a sequence number added (e.g. fred0.wav, fred1.wav ...). This allows you to select the number on which recording will start.

ENABLE METERS

Switches vu-meters on and off. Usually these are left on, but you can switch them off for a minor performance increase if you experience difficulties.

USE NOISE REDUCTION

Switches on / off LMS noise reduction (used to reduce hiss). Noise reduction data is initialised during silence analysis (see format dialog)

CLOCK DISPLAY

When recording from a soundcard, Audiotools displays a clock - this can either display the time elapsed since recording began or the current length of the current track.

Tips on using Audiotools

Top-n-Tail / Auto-track

Before recording with either of these methods, you should perform noise-floor analysis on a silent portion of audio by using Analyse i./p or Analyse file on the file dialog. This sets up the maximum and minimum levels for noise. You can also adjust these manually. Typically, these levels will be similar between similar media recorded using the same soundcard.

Noise reduction

Before using noise reduction you should perform analysis on a silent portion of audio by using Analyse i./p or Analyse file on the file dialog. The information generated (generally referred to as a noise profile) cannot be edited or viewed at the moment (this may be added later).

Speed issues

Some operations, such as noise-reduction, can take considerable amounts of processor power. If a computer is too slow to support it, this may lead to break-up of the sound when recording from a soundcard (but not from files). In extreme cases, Audiotools will detect that your machine is too slow and report an error. For some PC's there will be no alternative, but to perform a recording with auto-tracking and then noise reduce the individual files. These speed issues will be addressed by means of further code optimisation and by allowing more control over the slower components. If you want to improve your PC for using audio programs such as Audiotools, the best place to start is with your hard-disk and the IDE / SCSI controller. Basic recording operations are not processor intensive, but can be very hard-disk intensive. It is also advised that you look at the cache settings in Windows 95.

Version history

March 1998 v1.0 - First release version. Basic recording / playback and Top-n-tail / Autotrack facilities.

April 1998 v1.1 - Improved auto-tracking, improved interface feedback and added lms noise reduction. About box now reports registered user. File based operations accelerated, particularly during complex save operations such as Auto-Track. Removed embedded test data to reduce file size for release versions.

May 1998 v1.2 - Accelerated file operations, particularly for playback. Fixed a bug in "Analyse input". Added clock modes and disable meters capability. Moved enable noise reduction to "Format/Options". Added "Initial Sequence Number" (requested by Jeff Velt).

v1.21 - Fixed the "too slow" problem that came up during prolonged sessions.

Things yet to come

There's plenty of scope for more to be added to Audiotools.. I'm planning to add off-line track splitting for the next version and to look into other forms of noise reduction and manually configurable filtering. I'm also looking at interface improvements. Any suggestions, bug reports or requests for features can be emailed to me at amfish@globalnet.co.uk - I can't promise to add everything, but I'll see what I can do.

Shareware

Audiotools is shareware - it can be registered by credit-card through RegNet (http://www.swregnet.com/) for a sum of $15 US or through UK ShareReg (www.uksharereg.com/atools.html) for ú10 UK. UK ShareReg will also take Switch and can, for a small extra charge, handle postal dispatch of registration keys.

The unregistered version is limited to 5 minute recordings. Please register - it will allow Audiotools to develop into an affordable and poweful solution to creating audio tracks and sound effects.

Acknowledgements

Thank you to everyone who has registered so far - it makes the effort worthwhile. A special thank you also to Joel Curtis, Jeff Velt and Scott Born, all of whom have provided invaluable feedback and to Duncan Russell who supplied technical information on filtering and noise reduction.