Barry Hufker wrote on Sun, 01 April 2007 20:57 |
I have just done a sweep from 20 Hz. to 40kHz, at 96K and 24 bit. I then converted from 96k to 44.1 kHz at 24 bit. I used three methods: 1. Soundblade; Peak and Barbabatch. Of the three, Peak comes closest to the ideal of being "out" by 22050 Hz. It has a fairly smooth fade just before that frequency. Second is Barbabatch which extends a little more past 22050 with a lesser (not as steep) fade out. The worst plainly, simply, dramatically is the conversion by Soundblade. I don't believe this to be one by Izotope. I couldn't find that in my list of plug-ins if it did indeed come with the program. So the one written by Sonic is nothing less than terrible, extending well past 22050 and is sure to cause aliasing.
Barry
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Barry, I told Oliver Masciarotte from Sonic Studio about your measurements and he allowed me to post his reply here in this thread:
"Our SRC is designed to sound good, not fall within a old textbook example of anti-aliasing. In brief, all anti-image (when creating a file) and anti-alias (when playing back) measures are designed to reduce the audible artifacts of sampling.
The ?old school? thinking was that the designer tried to provide a flat frequency response in the passband, sever cut in the stopband (usually with a high order, low pass filter) and to hell with the group delay. A more modern approach, which we use, is to provide both flat frequency and phase response in the passband, controlled roll?off in the stopband and minimize overall group delay as much as possible. So, response above the Nyquist frequency is not severely cut, it is controlled, with an appropriate roll?off that reduces artifacts while preserving both passband ripple and, equally as important, phase response.
An interesting sidenote is that the poster seems to not have done any listening tests, since he says, ? and is sure to cause aliasing??Well, had he actually listened to these three versions, he would find they all sound different and he should pick his method/tool based on how it sounds with music, not solely based on measurements with tones."
I don?t want to add something here as long as I didn?t compare Barbabatch and soundBlade?s SRC by hearing. Hopefully I can do the comparisons this week an will tell my impression here again.