You can convert to quadrature by either sampling a signal at >= 2 * Nyquist and using the Hilbert transform, or using two ADCs 90 degrees out of phase. When yo

You can convert to quadrature by either sampling a signal at >= 2 * Nyquist and using the Hilbert transform, or using two ADCs 90 degrees out of phase. When you run two ADCs 90 degrees out of phase that introduces another source of error, due to timing jitter. There's no reason to bother doing this for audio signals because modern ADCs are more than capable of accurately sampling at audio rates.