Step 7: Modifying the Sound Effects
One of the great things about Tsunami Digital Sound Decoders is the ability to adjust the various sound effects to suit your ear and respond in the manner that you prefer.
Audio Mixer Controls
The Tsunami sound decoder provides up to 25 independent controls for setting the volume levels of each sound effect much like that of a modern sound studio mixing board. To set the sound level for a particular effect, set the corresponding CV to any value between 0 (zero volume) and 255 (maximum volume).
For the best sound quality, you will want to run the mixer as “hot” as possible (audio jargon for maximizing the volume level). First determine which sound you want to be the loudest (usually the whistle) and set its volume level to around 225. Then adjust all the other sound levels relative to the whistle volume. Finally, use the Master Volume Control, CV 128, to set the overall volume of the decoder to the desired level.
A certain level of prudence is needed when adjusting the mixer levels to avoid a condition known as ‘clipping’ or ‘limiting’ which occurs when the sum of two or more signals exceeds the capacity of the output channel. As its name implies, clipping results in the lopping off of the sound signal peaks and manifests itself as distortion accompanied with a level of clicking or popping sounds.
To avoid a clipping condition, consider which sounds are likely to be played at the same time and take care to ensure that their corresponding mixer levels are not set too high. For example, the whistle and exhaust chuff are usually heard together and you will likely want both to be as loud as possible. Rather than simply crank both sounds up to the maximum level, start with one mixer channel near, but not quite at maximum (this provides a little extra ‘headroom’) and then gradually bring up the second mixer channel setting to the desired level. If you start to hear some distortion, simply back down one mixer channel or the other until the distortion goes away.
Your Tsunami sound decoder has a 96dB dynamic range which is plenty for most audio work and as long as you keep the sound levels balanced in a prototypical fashion, you should have no problems.
Note that the Primary Mixer CVs are real time controls, meaning that any changes to their settings will be immediately reflected in the sound level. On the other hand, the Secondary Mixer levels are not real time. If you change their setting while the respective sound effect is playing, you will not hear a change in volume until the sound is turned off and started again.
Tsunami Steam Sound User’s Guide