Network Audio Players/Servers

Testing the CA1000 proved somewhat tortuous as the S/PDIF and USB digital inputs are not fully 'debugged'. On our early sample the digital filters are available from the menu but are not enabled (it sticks with 'Linear Phase/Fast'), incoming 24-bit files are effectively truncated to between 15/16-bits [see red trace, Graph 1] and the external inputs will not lock securely to sample rates above 176.4kHz. However, playback of 24-bit media held on the CA1000's internal storage is 'textbook' with all three digital filters fully enabled. In 'Line Out/Low Gain' modes the player offers a standard 2.05V maximum output, a 105.4dB A-wtd S/N ratio (this falls to 98.5dB via S/PDIF) and distortion that holds to ~0.005%/0dBFs (20Hz-20kHz) falling to a minimum of 0.0009% over the top 20dB of its dynamic range [Graph 1].

The Linear Phase filter trades significant pre/post echoes – time domain distortion – for a moderate 60dB suppression of stopband artefacts and very flat response that's within ±0.03dB from 20Hz-20kHz (CD/48kHz) and –0.35dB to 45kHz and 90kHz with 96kHz/192kHz media, respectively. The Minimum Phase filter has a gentler roll-off falling to –5dB/20kHz and –7dB at 45kHz and 90kHz, again with 96kHz/192kHz media, respectively. The Hybrid filter is closer to the Minimum Phase in execution but has steeper, sharper HF roll offs (–12dB/20kHz with CD) traded against a 60dB stopband rejection and minimal pre-echo in the time domain. Otherwise digital jitter is one area of 'interest' in the CA1000... Via S/PDIF (for all its other issues) jitter is a low 130psec but via the internal storage it rises to a high 1300psec/48kHz [see Graph 2, below], the complex sidebands clustered around ±210Hz, ±635Hz and ±1.05kHz. PM