Sound Manager: Digitizing, Down-Sampling, and Static

I get static and distortion when I digitize sounds. This happens when I record at low sound levels (soft music) with any application that uses the Sound Manager, including Apple's Sound control panel. The resulting static is louder than the originally recorded signal. The static appears to superimpose itself over the whole recording.

The issue occurs on both a Macintosh 840AV and a Macintosh Performa computer. I've tried different input devices, such as: a PlainTalk microphone, third party microphones, audio CDs, and video sources. I've tried several software programs including: the Sound Control Panel, SoundEdit Pro 1.0.5, SoundEdit 16, Fusion Recorder, MoviePlayer, and Digitrax.

The only program that consistently works without static is called Digitrax. It records fine at any bit-depth and any sampling rate. I can record a clean sound with Digitrax, but as soon as I edit it with SoundEdit Pro, static is introduced into the sound.

I have replaced logic board, clean installed system software, run Disk First Aid, replaced PlainTalk microphone, reinitialized the drive, reset PRAM and rebuilt the desktop. What is wrong?

The original recording is clean. The static you're getting comes from what is done to the sound when you digitize (edit) it. There is a known issue with the method that you're using. Recording in 16-bit 44kHz stereo audio and then down-sampling the file to an 8-bit 22kHz mono file will result in a lot of anti-aliasing artifacts (static).

The workaround for this issue is to record the file in 8-bit mode from the beginning instead of downsampling. However, you must keep in mind that any program which records in 8-bit mode such as Fusion Recorder, Sound Edit Pro, or the Sound Control Panel will introduce some noise with the signal. Other applications, such as Sound Sculptor, will allow you to record in either 8- or 16-bit mode, so the issue can be avoided. You may also want to make sure you are using the latest version of Apple's Sound Manager extension (v 3.1). It is no longer a separate extension in System 7.5 or later, but instead is built into the System file.

There is also a known issue when using QuickTime 1.6.1 and MoviePlayer to record 16-bit audio from an audio CD. The recording that results from this combination of software will have a lot of static. The combination of QuickTime 2.0 and MoviePlayer 2.0 fixes this issue.