Integrated Amplifiers

T+A’s longstanding synchronous upsampling filters are retained in the R 2500 R and have particular potency with CD playback. The ‘FIR Long’ [black, inset Graph with 1kHz-20kHz scale] and ‘FIR Short’ [red] filters are traditional linear-phase types while the mixed ‘Bezier/IIR’ interpolation [blue] and Bezier filters are minimum-phase types based on – you guessed it – Bezier polynomials. While these four filters have been a T+A staple for decades, its two ‘NOS’ (Non-Oversampling) options are a more recent addition. NOS 1 and NOS 2 [green] offer native conversion with no digital upsampling or filtering – much like the original Sony CDP-101 CD player [HFN Jan ’12] – and so offer almost perfect time domain behaviour (no ringing) albeit with a rolled-off treble of –3.6dB and –3.4dB/20kHz, respectively, with CD media. There’s almost no anti-alias rejection either, so ‘reflections’ of the music signal appear directly outside of the audio band, potentially causing IM distortion with low feedback amplifiers.

The ‘FIR Long’ filter shows strong pre/post ringing but offers fine rejection of aliasing images (102dB with CD), low phase distortion and a flat –0.3dB/20kHz response. ‘FIR Short’ has much reduced pre/post-ringing but also a limited 7.5dB rejection of images and a steep treble roll-off of –3.8dB/20kHz. ‘Bezier/IIR’ behaves like a slow/minimum phase filter with, again, poor image attenuation, slightly increased phase distortion and a +0.7dB/13kHz treble peak. PM