Taking Out the Thwack

The issue of "Thwack", or pushing your sound card into digital overdrive/overload, has been discussed in many forums over the last few years. It was never an issue with analogue or tape recording because the tape saturation of analogue has more of a sweetening effect (in small amounts) to modern music. The problem, not at all unlike the issue of a transistor guitar amp as opposed to a tube amp, is that when transistors are pushed or overloaded with voltage/sound output they produce a square wave as opposed to the saw tooth of tube/analogue. The result of a square wave to our ear (in most cases) is a brittle sound.

The reason it seems so easy to get "Thwack" sound card saturation is that wave volume is additive, which means that it adds amplitude to that which is already there. Basically if you have a recorded track that is right on 0 vu, the next recorded track will add to the output and push the card into "Thwack". Although 0 vu is the optimum quality level, you can see that more than 1 track at optimum results in "Thwack" and unusable sound.

Here is a process that will keep you well within most sound card output tolerances.

  1. 65% on the mike input seems to be a good starting point for mike level. You will have to experiment for the best results on your card. What you want is to get close to 0 VU on the recorded track.
  2. Record a track, then in the bars window, highlight it.
  3. Use the edit/audio/gain and select preset #4 Normalize. This will make sure that the recorded track is as loud as it can be without "Thwack". Process the track.
  4. Select preset #4 Cut -3dB. Process the track.

If you process each track similarly, you will find you have as much headroom as you need for all the tracks your system will handle.

It is much better if you use a mixer and route all sound (MIDI & sound card playback) through it, and then back to a tape deck or whatever for final mix. But MAKE SURE that in this setup you do not route the soundcard playback back into the soundcard again. This is where much of the sound bleed problem people complain about occurs.

Have Fun Recording

Braden
support@pgmusic

Last updated:  Tuesday, 13 October 2015

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