T+A HV Series User Manual

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T+A HV Series User Manual Manual pdf 63 page image

63Technical descriptionDigital filters / OversamplingOversampling The audio data on for example CDs is stored at a sampling rate of 44.1 kHz -i. e. for each second of music 44.100 sampled values are available for eachchannel. In the SDV 3100 HV the audio data read from the CD is „multiplied“to a higher sampling rate before it is converted back into analogue musicsignals. This process delivers a very much better, more finely graduatedsignal to the converter, which can then be converted with correspondinglyhigher precision. The raised sampling rate is a calculating process for whichthere are many different mathematical methods. In almost all digital audiodevices which exploit the advantages of increased digital sampling rate aprocess known as a FIR filter is employed for this purpose. At  we havebeen carrying out research for more than ten years, aimed at improving theoversampling process, because the standard FIR method has one drawbackto set against its indisputable advantages: it adds small pre- and post-echoes to the music signals. At  we have developed mathematicalprocesses (known as Bezier polynomial interpolators) which do not sharethis disadvantage. For this reason they should sound better and morenatural than the usual standard process. Since the calculating procedureemployed by us is considerably more complex than the standard method, theSDV 3100 HV features a digtal high precision floating point signal processor(DSP) which carries out the over-sampling process using special algorithmsdeveloped by .The freely programmable DSP which we use is capable of carrying out theoversampling process using any method of calculation. For this reason wehave implemented a slightly modified Bezier process (filters 3) in theSDV 3100 HV in addition to the pure Bezier process (filter 4), together withtwo variants of the standard process (filter 1 and filter 2). For moreinformation on the different processes please refer to the next section. Youcan switch between the various algorithms, then decide for yourself which ofthe filters gives the results you prefer.FIR long (Standard FIR Filter)The long FIR filter is the standard oversampling process in digital technology,offering extremely linear frequency response, very high damping, linearphase characteristics and constant group delays. The disadvantage is thepre- and post-echoes which are added to the signal. These „time rangeerrors“ tend to affect the music signal’s dynamics, precision andnaturalness, and reduce spatial orientation.Frequency response and transient characteristics of the long FIR filter