Why doesn't Analog Devices manufacture 32-bit audio converters?

Document created by BrettG Employee on Dec 3, 2012Last modified by BrettG Employee on Dec 5, 2012
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Several customers have asked lately if Analog Devices has any 32-bit audio converters in our product offering. At the moment, we do not. The reasoning for this is as follows:


A 24-bit converter has a theoretical noise floor of -144 dBFS (that is, relative to the full scale signal level), but in practice, a converter (ADC or DAC) never achieves that high performance. The very best converters on the market right now for 3.3 V audio systems only make use of about 22 bits (with the bottom 2 bits sitting in the noise floor of the converter) giving an effective noise floor of around -132 dB. Most cost-competitive converters have noise floors in the -100 dB to -120 dB range. Once the audio signal is in the analog domain, the 3.3 V full-scale signal path (consiting of PCB traces, resistors, capacitors, and op amps) has a practical noise floor of slightly below -130 dB. This residual environmental noise is due to natural factors like solar radiation, thermal noise, radio waves, and other "natural" sources of noise.


Some 32-bit converters are now available on the market, but in reality, the analog performance of these converters, and the environmental noise in the system, are still the gating factors of the overall system performance. Only about 22 bits carry signal and the remaining 10 bits are simply lost due to the noise floor of the "weak links" in the signal chain. So, it can be argued that having a 32-bit converter in a 3.3 V audio system is really not adding any value compared to what a 24-bit converter would do, at least when the performance limits of current converter technology are taken into consideration.


There is, however, some merit to having a 32-bit DSP core in an audio system, because calculations done in the digital realm are subject to quantization noise and minor calculation errors. For that reason, it can be worthwhile to have a 32-bit DSP core surrounded by 24-bit audio converters (with dither performed during the bit depth conversion stage of the system).