|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
65.19.76.104
In Reply to: RE: Spectrum Plot for CD rip and 24/96 download - pics posted by cfraser on July 12, 2014 at 11:21:43
That noise is a symptom of something wrong. It should not be there. Without understanding the root cause it is impossible to say whether there is a sonic problem. I have transferred a bunch of old master tapes and it's been my usual experience that ones with funny noise peaks on them don't sound as good as clean ones. Usually, filtering out the noise peaks makes things somewhat better. But the best recordings don't start out or gain these unwanted artifacts.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Follow Ups:
The peak is -60dB down compared to what is in the 0-1kHz rangeso it is questionable whether one can hear it. There are both masking effects and ear sensitivity going against audibility. Given the age of most audiophiles (or Jimmy Page), the odds are further reduced. I agree it would be more satisfying to know that this noise pollution was not there, but that would be listening with one's brain, not one's ears.
A quick experiment: upsampling the 16/44.1 to 16/96 or 24/96 and listen whether this upsampled file gets to sound as good as the "orginal" 24/96 remastering. As you pointed out earlier,one benefit of higher sampling frequency files is to move reconstruction filters to much higher frequencies than what is otherwise possible with 44.1kHz. Nothing to do with the actual file content.
One caveat: we do not know how much high frequencies these hires remasters contains because the posted spectra have been averaged over 60 seconds. As otherssuggested, it would be more informative to see spectrogram to see if there are times at which there is much more high frequency content in the high res file than in the CD file. It is not like Bonham never hit the cymbals!
Normally, I use a 65K FFT for spectrum averaging. But my software allows other sizes as well, plus different windows. (Soundforge 10). I also have iZotope RX and this includes a spectrum plot of time (X) vs. Frequency (Y) vs. intensity (Z, i.e. color). The size of the temporal resolution can be adjusted but there is the inescapable tradeoff of time resolution vs. frequency resolution.
With these spectrum plots it is very easy to see high frequency noise and to distinguish it from high frequency musical sounds. In addition, one can edit the spectral plots to easily remove unwanted noises, even to the point of removing notes out of a chord or removing guitar string squeaks.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Unlikely your software will allow to do a FFT with 60*96,000 points. There's a bunch of averaging going on that's a function on how the analysis is setup (number of points in the window, window overlap,...) The loss of frequency resolution that comes with shorter windows does not matter since energy gets summed up in each frequency band. A delta f of 1Hz or of 10Hz will still tell the story of whether there's significant energy at higher frequencies.
It looks like you posted in the wrong place.
I agree that it's unlikely that Abe Collin's FFT averages over 60 seconds. Possible, but not likely. I know that my FFT averages over 65K points with my usual settings and this corresponds to about 2/3 of a second at 96 kHz. The points in the window are weighed with the central points counting more according to a formula that smooths out the plot. I generally use a Blackman-Harris window.
There are a lot of other issues involved with interpreting FFT plots, such as "FFT gain" which is a measure of how the noise floor varies in FFT plots according to the window size and window type. If Abe wanted to, he could calibrate his FFT gain by creating a test file with a 28 kHz tone and adjust the level of this tone to where the FFT shows it at the point on the suspect download file. A little knowledge can be a dangerous thing, but I'm confident that Abe Collins knows enough to figure these things out, if he hasn't already done so.
BTW, I have other software that I use that uses 8 million points. I've used this to do convolution by transferring to the frequency domain and multiplying. In addition, my player routinely does convolution at 2.8 MHz sampling rate with a time period of about 1 second (over 2,000,000 samples). I presume the software uses FFTs, to avoid the necessity of more than 10^14 multiplications per second using a simple time domain approach, which even if my hardware could do would run up a huge electric bill.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: