Rotel RCD-955AX and RCD-965BX CD players RCD-955AX Measurements

Sidebar 1: RCD-955AX Measurements

Beginning with the multi-bit Rotel, the frequency response (fig.1) was virtually flat across the audible range, with only a small amount of ripple in the upper octaves—ripples characteristic of machines using Philips digital filters. The 1kHz squarewave in fig.2 is also typical of players using linear-phase digital filters, and although pre-emphasized CDs are in the distinct minority, the virtually flat de-emphasis response (not shown) guarantees that they will be properly balanced in playback.


Fig.1 Rotel RCD-955AX, frequency response at –12dBFS into 100k ohms (right channel dashed) (0.5dB/vertical div.).


Fig.2 Rotel RCD-955AX, 1kHz squarewave at 0dBFS (4ms time window).

The crosstalk from the left to the right channel is shown as the top curve in fig.3; the right-to-left crosstalk is the bottom curve. The separation indicated here is not exceptional, but unlikely to be audibly significant.


Fig.3 Rotel RCD-955AX, channel separation (10dB/vertical div.).

Fig.4, the spectrum of the RCD-955AX reproducing a –90.31dB dithered tone at 1kHz, shows some negative deviation from linearity but no significant artifacts other than a hint of third-harmonic at 3kHz. The linearity is more clearly shown in fig.5, where the deviation at –90dB is just under 2dB. Only the right channel is shown; the left was virtually the same. Listening to the fade-to-noise with dither signal from the RCD-955AX produced only one or two minor whistles at what I would estimate to be well under –80dB. They were well below the primary tone in level. The overall linearity of the RCD-955AX is very good for a multi-bit player in this price class.


Fig.4 Rotel RCD-955AX, 1/3-octave spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with 16-bit CD data (right channel dashed).


Fig.5 Rotel RCD-955AX, right-channel departure from linearity (2dB/vertical div.)

The noise spectrum of the player's output when playing a "digital silence" track in fig.6 has no artifacts worth noting. It is worth noting, however, that we've recently become aware that some players are designed to actually mute the output of their D/A converters when presented with an all-zero digital signal—a practice which enhances their measured S/N ratio. That might be the case here; the measured spectrum (not shown) with the player in Pause was virtually identical to that in fig.6. In any event, this figure does show the noise contribution of the analog stages to the output to be negligible.


Fig.6 Rotel RCD-955AX, 1/3-octave spectrum of silent track ("digital black"), 30Hz–200kHz.

Fig.7 shows a 1kHz, undithered tone at –90.31dB from the 955. The desired stairstep sinewave is evident, though the nearly inevitable noise makes interpretation difficult. And in fig.8 the response of the 955 to a 19+20kHz, 0dB signal shows no significant IM artifacts. The aliasing tone at 24.1kHz is commonly seen in players using Philips technology; the relatively slow-slope filter in these machines—a plus for a number of reasons—cannot completely eliminate this tone. It would only be a potential problem when used with an amplifier having marginal high-frequency stability.


Fig.7 Rotel RCD-955AX, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit CD data.


Fig.8 Rotel RCD-955AX, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 100k ohms (linear frequency scale).

The RCD-955AX is non-inverting at its analog outputs, neither of which had measurable DC offset. Its output impedance is just over 198 ohms on both channels.—Thomas J. Norton

Rotel of America
54 Concord Street
North Reading, MA 01864-2699
(978) 664-3820

Catch22's picture

Man, I hated to see him go. Couldn't you bring him back? Maybe put him on double secret probation and make him grow a beard as punishment?

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