The number of bits in a PCM digital transmission system determines the maximum SNR (signal to noise ratio) that can be achieved using that transmission system.
If you wish to include the distortion produced by an audio component, use SINAD instead of SNR.
Example 1 (SNR to ENOB):
The Benchmark DAC3 has a SNR of 126 dB unweighted. This SNR equates to an ENOB of 20.6 Bits.
In other words the DAC3 has the same signal to noise ratio as a perfect 20.6 bit converter.
Example 2 (SINAD to ENOB):
The Benchmark DAC3 has a SINAD or THD+N of 113 dB at full output. This SINAD equates to an ENOB of 18.5 bits.
In other words, the DAC3 achieves the THD+N performance of an ideal 18.5 bit converter.
Example 3 (Amplifier SNR to ENOB):
If we have an analog component, such as an audio power amplifier, we can determine the SNR performance in terms of ENOB. The Benchmark AHB2 power amplifier achieves a SNR of 132 dB in stereo mode. If we plug this into the calculator, we find that this equates to 21.6 bits.
In other words, the AHB2 can achieve a SNR that is equivalent to that of a 21.6 bit system. Notice that this is sufficient to deliver the full 20.6 bit performance of the DAC3 (calculated in example 1) to the speaker terminals.
The actual ENOB delivered to the speaker terminals will be 20.4 bits due to the summation of the noise of the DAC3 with the slightly lower noise of the AHB2, but this detail is beyond the scope of this application note. As a general rule of thumb, the amplifier should be at least 1 bit better (or 6.02 dB better) than the signal from the DAC if you want to deliver the full performance of the DAC to the loudspeakers.