Rate and Hertz Hz

Many effects are modulated and can periodically vary over time. The period of this variation is measured in cycles per second, or Hertz (Hz), the measurement used in AQD for the Rate controls on the plug-ins. For example, 1 Hz is one cycle per second, 10 Hz is ten cycles per second, and 0.1 Hz is one cycle every ten seconds. This is a very logical and easy way to talk about periodic variation, and it is very easy to instantly see that 2 Hz is twice per second and 7 Hz is seven times per second. However, it is less intuitive once the period drops below once per second. In this case, the smaller the fraction, the slower the period. You can quickly calculate the proper Rate to set by dividing one by the period you want. So, to get a period of once every seven seconds, you d divide one by seven (1/7) and get a Rate of 0.143 Hz. The Rate range in ACID is from twenty rimes a second (20 Hz) to once every 1,000 seconds (almost seventeen minutes 0.001 Hz). 

Many of the effects that modulate or cycle over time (for example, Delay, Flange/Wah-wah, and Stutter) can easily and effectively be synchronized to the beat of a song. The Rate for these effects is measured in cycles per second and project tempo is set to beats per minute (bpm), so divide 60 seconds in a minute by the number of beats per minute to get the delay in seconds. By default, ACID projects are 120 bpm, so  

you need to convert this into cycles per second  

if you wanted a wah on every beat, you d need a Rate of 2.000 Hz, or two cycles per second. For a 140 bpm project, we get 2.331 Hz, and for 100 bpm, a rate of 1.667 Hz. Flanges often have much longer cycles that you might want to synchronize in terms of measures. Since tempo is typically annotated in terms of a quarter note = one beat and, by default, ACID has four beats in a measure, you only have to multiply the number of seconds by four and convert to Hertz (Hz). 

60 seconds / 155 bpm = 0.387 seconds for one beat 4 beats a measure = 0.774 seconds for one measure 

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