Technical Details for Sound-Recorder

SoundRec was designed assuming usage of the Alsa arecord tool to capture analog audio from your sound-card. The arecord utility records to WAV format, and does not save to compressed formats such as OGG or MP3. (There may be ways to do it, such as piping to a converter, but it was not obvious (to this casual observer anyway), hence SoundRec makes it easier.) This is OK, because once we have the audio in some digital format, we can convert it to others using widely available converter utilities.

In particular, if you select to save your recording in OGG or MP3, then SoundRec automatically calls the selected conversion tool, and deletes the WAV file after the conversion completes. This typically results in a massive reduction in file-space.

SoundRec spawns-off the conversion task in the background under a reduced priority (niced), so as not to interfere with continuing operations. The conversion process requires some time, depending on the length of the recording. For example, converting a 20 minute WAV file may require a half-minute or so, to convert to OGG or MP3. The conversion status will be indicated in your text window, assuming you launched SoundRec from a terminal window.

Before recording, you should check the sound-level. You can do this by clicking the Levels button on the center-right of the Recorder panel. It will pop-up a small window with LED VU meters. The green LED's indicate the RMS level. The Red tick-mark is a peak-hold indicator. It indicates the peak value during the last second. It is important that the peak value stay below the 0-dB point, to avoid clippling the audio. When you press the Record button, the VU meter goes away, to free up the sound port for the arecord utility.

Often you will see no significant input (just sound-card noise below -40-dB), even though you believe you are applying sound to your mike or line-in jack. You will get blank recordings in this situation. If this happens, you need to change settings on your computer's Volume Control or Mixer panel. Often you will find this under the System / Preferences / Personal / Volume Control or similar menu. You need to make sure your Mike or Line-Input are enabled, and their volumes are up. Also, make sure your audio source is plugged into the correct sound-card jack on your PC. The VU meter display is helpful while trouble-shooting your system settings, because it gives immediate feedback when you finally toggle the right setting and get it right.

Compiling SoundRecEd -

Compilation commands are in the Readme.txt file, as well as the comment-header of the two tools, respectively. Graphics are based on OpenToolKit - a very small GUI-toolkit. To compile, get OTK-lib from:

Technical Discussion about Sound-Editor

Sound-Editor operates natively on WAV files. It can convert them to OGG or MP3 on save-out. It converts OGG or MP3 files to temporary WAV files on read-in. However, since OGG and MP3 are lossy compression methods, the audio will be degraded each time it is compressed, decompressed, and re-compressed. For the casual listener, one or two such cycles may not audibly degrade the sound, so it makes sense to provide this capability. However, repeated re-compression cycles will eventually produce noticeable degradation, certainly as far as audio purists are concerned. For best quality, it is recommended to keep all source files in WAV format until the final save.

It would be beneficial to develop a lossy compression technique in which the losses do not accumulate beyond the first compression cycle. Then audio could be stored indefinitely in compressed form, edited, and re-saved compressed, without losing much quality.

Other Platforms

The Sound-Rec-Ed GUI's will work on other platforms besides Linux, such as Sun Solaris, Mac OS-X, and Microsoft Windows. Just recompile the GUI's on your platform. However, the commands for the underlying sound-tools will need to be found and adjusted accordingly. See Configuring Sound Tools. If anyone identifies the appropriate commands on any of these other platforms, please send me a note (, and I will post the settings here.

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