A wah wah is a sound effect that imitates the sound of the syllable "wah".
A wah wah can be produced by adding gain to an interval of high frequencies in the signal and gradually moving that interval down and then up the frequency spectrum. During the wah wah, the gain to the high frequencies will gradually change to a gain in the mid and then the low frequencies and will then return to the mid and high frequencies.
Generating the wah wah sound
On brass instruments, the wah wah can be produced by muting and unmuting the bell.
A wah wah can be engineered by sending the signal through a peak filter or a band pass filter, gradually shifting the filter down and up the frequency spectrum, and mixing the output of the filter with the original signal.
Wah wah parameters
The following are some wah wah parameters.
- The wah wah could be periodic and follow the tempo of a song. A software generated wah wah may then have a rate of oscillation (LFO rate) or time of its cycle. For example, a song with a tempo of 75 beats per minute (800 ms per beat) may use a wah wah rate of 1000 ms / 800 ms = 1.25 Hz. In this wah wah, the muting or the move of the band pass filter may take 100 ms each down and up and the rest of the time may be spent muted (filter at the bottom of the frequency range) or unmuted (filter at the top of the frequency range).
- As the band pass filter moves down and up the frequency range, both the top and bottom cutoff frequencies – where the filter starts and stops before returning – impact the sound of the wah wah. How these two frequencies are chosen however also affects how quickly the filter moves up and down. On an acoustic guitar recording, with the timing parameters above, the wah wah filter may move for example between 2 kHz and 300 Hz.
- The width of the band that is allowed by the filter also impacts the wah wah. A notable wah wah can be produced on the same acoustic guitar with the above parameters and with a band pass filter with a width of, say, 500 Hz.
Auto wah wah
An auto wah is a wah wah that is triggered similarly to a compressor. Rather than having a fixed rate of oscillation, the wah wah effect sounds after the sound magnitude exceeds a certain threshold.