On Mon, 2009-02-16 at 10:50 -0700, Bearcat M. Şandor wrote:> ok, so i'm confused. If you're saying that upsampling is generally a bad > thing why does one pay extra for it in a product like this: > http://www.meridian.co.uk/product-model/g-series/g082-upsampling-compact-disc-> player.aspx ? One probably gets upsampling whether he pays extra or not. As I understand it there is a problem inherent issue with D/A conversionin that you have to stop the clock used to run the D/A converterappearing on converted analogue output. When the sampling rate has been chosen to give a nyquist frequency onlyslighly above the maximum frequency you intend to reproduce you thedesigner has to implement a very steep filter in analogue components. For CD this is the case - 44.1Khz sampling rate, 22.05Khz nyquistfrequency and you want to reproduce the whole human hearing range. If instead the sampled data is upsampled to a higher frequency the clockrate of the D/A converter is increased to match and the slope of theanalogue filter can be more gentle. Upsampling does not enable you to hear anything not on the CD. On theother hand an insufficiently steep analogue filter could cut into theaudio band so an oversampling player may play all of the information onthe disk and not just most of it. What it sounds like, of course, depends on the quality of the upsamplingalgorithm - there are good and bad of those. Back to the original issue with the sound card - most of the integratedcards these days seem to be optimised for 48Khz rather than 44.1Khz. Itmay also be the case that the hardware upsamples everything a multiple,for example 96Khz. Perhaps the algorithm they implement in hardware isbearable when the sampling rate a multiple (i.e. 2X for 48 to 96) andpretty poor when not (i.e. 44.1 to 96) and the ALSA algorithm is abetter one. _______________________________________________Linux-audio-user mailing listLinux-audio-user@xxxxxxxxxxxxxxxxxxxxxxxx://lists.linuxaudio.org/mailman/listinfo/linux-audio-user
