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In Reply to: RE: Attribution error? posted by audioengr on January 28, 2015 at 11:07:43
" ...it is really the 192 digital filter that makes 24/192 sound good, and only a little bit the higher sample-rate?"
This is simply not true. Furthermore, this oversimplifies the problem and misses the essence of how digital audio works. There are two filters involved, one used in recording and one used in playback. These filters will have different effects on the analog output that one hears.The record filter used for 44 kHz sampling has an impossible task to do: it must severely attenuate audio signals above 22 kHz or there will be aliasing distortion which will corrupt the purity of musical tones, it must have a narrow transition band so that it won't remove high frequency content and strip instruments of their natural brilliance and air, and finally it must have a wide transition band so that any ringing is short term and doesn't disrupt perception of imaging and sound stage. These criteria are mutually incompatible at 44.1 kHz. If one uses a recording filter designed for 192 kHz sample rate at 44.1 there will be severe aliasing distortion. This will be easily seen on a spectrum plot of a square wave as spurious tones below the fundamental frequency, and heard as "fuzz" on the sound that changes in character with a slight deviation of square wave frequency. If one listens to a square wave sweep tone with aliasing one can easily hear "birdies" going down in pitch, something that does not happen with proper filtering. Of course, these effects also happen with music.
The playback filter will not be able to undo the effects of the recording filter, the best it can do is not make matters worse. It can also change the type of distortion one gets in some cases, i.e. mild aliasing or mild ringing can be reduced by rolling off highs. Whether this is an improvement or not will depend on the original recording, the playback system and the listener's tastes.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Edits: 01/29/15Follow Ups:
Aliasing distortion is not a particular issue IME, only in measurements and on paper. In real-life, the analog filters and system filters it nicely. Try a NOS DAC sometime.
You are confusing alias distortion with image distortion. Alias distortion occurs when digitizing an analog signal or downsampling a digital signal. Image distortion occurs when upsampling a digital signal or converting it to analog. These have very different audible effects. With 44 Khz digital, alias distortion creates spurious frequencies in the band below 22 kHz. Image distortion at 44 kHz creates spurious frequencies in the band above 22 kHz. Alias distortion is grossly audible with test tones and not difficult to hear on music with lots of high frequency content that should have been filtered. Image distortion is harder to discern unless there is a lot of high frequency non-linearity on the part of the playback chain.
I base my comments on both theory and practice. I have generated test dones and done various sample rate conversions and measured and listened to the results. I have done the same conversions with music and listened to the results. It is not particularly hard to hear these effects if one experiments with sample rate conversions, starting with a pure analog signal or a high resolution digital file. It is much harder, if not impossible, to isolate these effects by purchasing the same recording in multiple formats because there is no visibility to what was done by the mastering engineer.
The filtering damage that Neil Young is concerned about happens in the recording process at 44 Khz. There is no magic that his or any other player can apply to restore the music that was thrown away and/or butchered during the conversion to 44 kHz.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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