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Microphone Month 5

Are All Converters “1-bit”?

Q: Someone told me that way down underneath, all converters are actually 1-bit designs. Is this true?

A: It is true that, at their root, many modern converters do use 1-bit technology.

Delta Sigma Modulation (a.k.a. 1-bit) is the “secret sauce” behind technologies such as DSD (SACD, etc.). What isn’t as commonly understood, however, is that nearly all modern converters use Delta Sigma Modulation. After the modulator they filter and decimate the data to build the PCM words at our desired sample rates. DSD records the data off the modulator, prior to this filtering. As such, DSD signals can be filtered later to create standard PCM audio data. DSD signals are also generally filtered upon playback to prevent too much ultra-high frequency audio information from being passed on to analog amplifiers as they often aren’t designed to respond desirably to it.

Currently typical Delta Sigma Modulators found in our audio products operate in ranges (meaning their sample rates are) between 2MHz and 6MHz. The “sample rate” you set on your PCM-based audio equipment merely tells the device what the final result will be at the output of the converter, after filtering.

A more modern adaptation of 1-bit recording has designers now exploring “low bit” recorders. These employ similar Delta Sigma Modulators, but instead of only 1-bit, they are able to generate two or four bits in parallel.

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