Preliminary Technical Data WM8788
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PTD, December 2011, Rev 2.3
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TERMINOLOGY
1. Signal-to-Noise Ratio (dB) – SNR is the difference in level between a full scale output signal and the device output
noise with no signal applied, measured over a bandwidth of 20Hz to 20kHz. This ratio is also called idle channel noise.
(No Auto-zero or Mute function is employed).
2. Total Harmonic Distortion (dB) – THD is the difference in level between a 1kHz reference sine wave output signal and
the first seven harmonics of the output signal. The amplitude of the fundamental frequency of the output signal is
compared to the RMS value of the next seven harmonics and expressed as a ratio.
3. Total Harmonic Distortion plus Noise (dB) – THD+N is the difference in level between a 1kHz reference sine wave
output signal and all noise and distortion products in the audio band. The amplitude of the fundamental reference
frequency of the output signal is compared to the RMS value of all other noise and distortion products and expressed
as a ratio.
4. Channel Separation (L/R) (dB) – is a measure of the coupling between left and right channels. A full scale signal is
applied to the left channel only, and the right channel amplitude is measured. Next, a full scale signal is applied to the
right channel only, and the left channel amplitude is measured. The worst case channel separation is quoted; this is
the difference in level between the full-scale output and the cross-channel output signal level, expressed as a ratio.
5. Power Supply Rejection Ratio (dB) – PSRR is a measure of ripple attenuation between a power supply rail and a
signal output path. With the signal path idle, a small sine wave ripple is applied to power supply rail. The amplitude of
the supply ripple is compared to the amplitude of the output signal generated and is expressed as a ratio.
6. All performance measurements are carried out with 20kHz AES17 low pass filter for distortion measurements, and an
A-weighted filter for noise measurement. Failure to use such a filter will result in higher THD and lower SNR and
Dynamic Range readings than are found in the Electrical Characteristics. The low pass filter removes out-of-band
noise; although it is not audible, it may affect dynamic specification values.
