Astell&Kern ACRO CA1000 Digital Audio Player Lab Report

Lab Report

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


THD vs. 24-bit digital level over 120dB range (1kHz, black; via S/PDIF, red dashed; 20kHz, blue)


High resolution 48kHz/24-bit jitter spectrum from internal storage, zoomed to ±2kHz. Markers (blue) identify 72 individual sidebands

Maximum output level / Impedance 2.05Vrms / ohm
A-wtd S/N ratio (S/PDIF / Storage) 98.5dB / 105.4dB
Distortion (1kHz, 0dBFs/–30dBFs) 0.005% / 0.007%
Distortion & Noise (20kHz, 0dBFs/–30dBFs) 0.005% / 0.001%
Freq. resp. (20Hz-20kHz/45kHz/90kHz) +0.0 to –0.0dB/–0.4dB/–0.3dB
Digital jitter (48kHz/96kHz/192kHz) 1300psec / 400psec / 80psec
Resolution @ –100dB (S/PDIF / Storage) +5.6dB / ±0.1dB
Battery specification 3.8V/8400mAh Li-Polymer
Dimensions (WHD) / Weight 105x45x149mm / 0.9kg
Price £1999

Seoul, South Korea
Supplied by: Armour Home Electronics, Herts
01279 501111