Digital Source Reviews

For these measurements, the P-1A and P-3A were both powered from the Monolithic Sound P³ supply. The P-3A's D/A converter didn't invert absolute polarity with its front-panel LED illuminated green, but did do so when the LED was red. It had a maximum output of 2.373V RMS, just under 1.5dB higher than the CD standard of 2V, with an output impedance below 1 ohm across the audioband. Channel separation (not shown) was superb, at better than 120dB below 400Hz, but with capacitive coupling between the channels reducing this to a still excellent 87dB at 20kHz.

With normal signals, the P-3A's frequency response was flat (fig.1, lower trace above 1kHz); but with a pre-emphasized signal, there was no corresponding de-emphasis applied (fig.1, upper trace above 1kHz). As a result, the small number of pre-emphasized CDs will sound very shrill.

Fig.1 Perpetual Technologies P-3A, frequency response with (top) and without (bottom) de-emphasis at -12dBFS (right channel dashed, 1dB/vertical div.).

Fig.2 shows a 1/3-octave spectral analysis of a dithered 1kHz tone with resolutions of 16 bits (top) and 24 bits (bottom). There are no power-supply-related spuriae to be seen! The drop in the noise floor associated with the increase in bit depth is 21dB in the treble and still 17-18dB in the midrange, which suggests that this inexpensive converter has a dynamic range equivalent to almost 20 bits—about the best I have measured! This superb dynamic range can also be seen in fig.3, which shows a wider-band spectral analysis with the processor decoding 16- and 24-bit "digital black." (As with some other digital products I have measured, the P-3A picked up RF interference from the computer monitor, so the latter was switched off while the data were being collected.)

Fig.2 Perpetual Technologies P-3A, 1/3-octave spectrum of dithered 1kHz tone at -90dBFS, with noise and spuriae, 16-bit data (top) and 24-bit data (bottom). (Right channel dashed.)

Fig.3 Perpetual Technologies P-3A, 1/3-octave spectrum of "digital black," with noise and spuriae, 16-bit data (top) and 24-bit data (bottom). (Right channel dashed.)

Linearity error (fig.4) was also superb; the low level of analog noise meant that the measured error didn't reach +3dB until -115dB or so. As a result of the nonexistent linearity error and the low noise floor, the P-3A's reproduction of an undithered 1kHz sinewave at -90.31dBFS (fig.5) was essentially perfect. Increasing the word length to 24 bits gave a pretty good facsimile of a sinewave with this very-low-level signal (fig.6).

Fig.4 Perpetual Technologies P-3A, departure from linearity, 16-bit data (2dB/vertical div., right channel dashed).

Fig.5 Perpetual Technologies P-3A, waveform of undithered 1kHz sinewave at -90.31dBFS, 16-bit data.

Fig.6 Perpetual Technologies P-3A, waveform of undithered 1kHz sinewave at -90.31dBFS, 24-bit data.