Frequency foldback

My suggestion is to open the pdf datasheet of any prospective switcher IC and carry out a text search (Ctrl + F) for the world foldback. If you find it, question the vendor about its full impact before you select the part for your application. Foldback is, in general, a good idea in terms of protecting the converter under abnormal conditions, but it should be used very judiciously so as not to impact normal behavior. For example, the Simple Switcher family has a hidden second-level current limit protection at which frequency foldback (or skipped pulses) occurs. But that trip level can only be encountered under very severe conditions—namely, a sudden overload with a completely incorrectly sized inductor that hard-saturates in the process. At other times it is not encountered and doesn t therefore interfere. It is considered transparent to all but the most novice engineers. And that is what I consider the right type of foldback. 

Hypercardioid microphones offer somewhat greater rejection of off-axis sound, but usually at the expense of frequency response and/or polar pattern smoothness. A few units do provide uniform frequency response from all directions, but sometimes the truth they tell about ambient conditions is less desirable. Lack of polar pattern smoothness can be a hazard in live performance foldback systems. An unexpected off-axis lobe maybe pointed at a nearby high-level loudspeaker. Some foldback applications have demonstrated higher gain before feedback using omnidirectional microphones with extremely smooth polar frequency response. 

The ADC needs at least two samples per waveform cycle in order to represent the frequency of the sound if not, then the frequency information is lost. Digital recording systems place a low-pass filter before the ADC in order to ensure that only signals below the Nyquist frequency enter the converter. Otherwise, the conversion process creates foldback frequencies, thus causing a phenomenon known as aliasing distortion (Figure 1.3). 

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