The flanger extends the phasing effect by also adding a pitch shifter [Pitch shifter ] , in other words, a circuit capable of increasing or decreasing the signal's tonality (the classic pitch shifting example is when you accelerate or decelerate the roll of a magnetic ribbon; in its early days, this effect was created by using an analogue reel recorder). To give a practical explanation of this phenomenon let's consider (as usual) a sinusoid at a certain frequency level recorded on a magnetic ribbon. By increasing the ribbon's speed we'll see that the sinusoid gets reproduced more quickly, which basically means that the sinusoid's frequency increases. The following is a logical scheme of a flanger:
We can see how the LFO pilots both the delay module and the pitch shifter module.
The following is a sound to which a flanger effect has been applied: