Sonographe SD-22 CD player Measurements

Sidebar 3: Measurements

The SD-22's frequency response (fig.1) is flat over most of the range, though its definite high-frequency rolloff beginning about 6kHz would likely translate into some softness in the upper octaves. The ripples in the top two audio octaves are typical of the Philips digital filter used. In fig.2, the SD-22's de-emphasized response tracks the HF rolloff of the player as a whole. The squarewave response in fig.3 is typical of the players in this group—a good rise-time combined with the moderate ripple indicating a linear-phase digital filter, though more overshoot than the other players. The crosstalk in fig.4 (only left to right is shown; right to left was virtually identical) was higher than that from the other players, though still unlikely to be audibly significant.


Fig.1 Sonographe SD-22, frequency response at 0dBFS (right channel dashed, 0.5dB/vertical div.).


Fig.2 Sonographe SD-22, de-emphasis error (right channel dashed, 0.5dB/vertical div.).


Fig.3 Sonographe SD-22, waveform of 1kHz squarewave at 0dBFS (2ms time window).


Fig.4 Sonographe SD-22, channel separation (10dB/vertical div.).

Fig.5 shows the SD-22's output when decoding a –90.31, dithered 1kHz sinewave. Some low-level non-linearity is present, along with some (likely) power-supply–related noise at 60Hz and 180Hz—though these are well below –100dB. The bump in the trace at 7.5kHz is suspicious, however, perhaps indicating some idling tones. Linearity is shown in figs.6 (left channel) and 7 (right). The left-channel response is fair, within 2dB down to –110dB, but the disappointing right channel shows a quite high deviation below –90dB. Both channels show unusual nonlinearity for a 1-bit player, most of which pass this test with flying colors. (I found this result so surprising that I ran it three times on three different days—with the same outcome each time.) The fade-to-noise with dither track from the CBS CD-1 test disc did not produce a particularly clean result, with several whistles (below the signal level) popping up intermittently as the signal faded to noise. The SD-22's noise spectrum (fig.8) shows the rising noise level above 20kHz typical of the other 1-bit machines, the minor power-supply noise artifacts at 60 and 180Hz, and little else of significance apart from the idling tone at 7.5kHz.


Fig.5 Sonographe SD-22, spectrum of dithered 1kHz tone at -90dBFS, with noise and spuriae (right channel dashed).


Fig.6 Sonographe SD-22, left-channel departure from linearity (2dB/vertical div.).


Fig.7 Sonographe SD-22, right-channel departure from linearity (2dB/vertical div.).


Fig.8 Sonographe SD-22, spectrum of digital black with noise and spuriae (1/3-octave analysis, right channel dashed).

The SD-22's waveform of a 1kHz, –90.31dB undithered tone is presented in fig.9. The player's high noise floor makes this graph's interpretation a bit difficult, with little evidence of the desired stairstep response. The Philips digital filter has less stop-band rejection than most of the Japanese filter chips, as can be seen from the 19+20kHz (0dB) IM spectrum (fig.10). The cursor shows the 24.1kHz aliasing product to be 55dB down, however, which is still good.


Fig.9 Sonographe SD-22, waveform of undithered 1kHz sinewave at -90.31dBFS.


Fig.10 Sonographe SD-22, HF intermodulation spectrum, DC-30kHz, 19+20kHz at 0dBFS, 100k ohm load (linear frequency scale, 10dB/vertical div.).

The Sonographe inverted polarity at its main outputs, with 0V DC offset from both channels. As noted by CG in his review, its output was significantly lower than those of the other players here, producing 0.732V (left channel) and 0.733V (right) in response to a 1kHz tone at 0dB, these 8.7dB below the standard CD playback level of 2V RMS. Its output impedance measured 624 ohms (left channel) and 621 ohms (right).

Not unexpectedly, the measured results did not correlate well with the listening tests. In particular, measured low-level linearity, as it has a number of times in the past, did not follow the subjective results with any consistency. One of the top-rated players in the subjective tests was the Sonographe and its disappointing performance on this test showed a distinct difference between channels.—Thomas J. Norton

Conrad-Johnson Design Inc.
2800R Dorr Avenue
Fairfax, VA 22031
(703) 698-8581

hollowman's picture

I was just looking at the print issue this review was in (Feb 1992).
The Sonograph was one of several CDPs CG and TNJ reviewed in a "shootout" of mid-priced players.
The Sonograph review above makes much more sense in the CONTEXT of ALL the reviewed units.
One important point being that the Sonograph was worst-measuring of the set.
Another important aspect was that each of the CDPs utilized different DAC and DF topologies (Bitstream, multibit, various oversampling rates, etc.).

So ... JA (or to whom it may concern): please publish rest of review! Thx!

hollowman's picture

BTW ... I noticed that Stereophile used to publish squarewave in its Measurements (as in this 1992 review) .
I haven't seen them in over two decades (??). When and why did Stereophile quit this practice?

watchdog005's picture

This CD player is like owning a $20,000 turntable cartridge combo. Sweet sounding analog without a trace of digital harshness. It's rare and it's a keeper. Audio CD's sound better on this unit then they do on an expensive unit that plays SACD's so it makes a great addition to your system even if you own a modern SACD or DVD audio system. These are well built and hard to find so grab it if you can find one.