A few weeks ago I posted a comment about a downloaded track from iTunes - Bridge: Summer, RLPO Groves - http://www.for3.org/forums/showthrea...CD-remastering I have since revisited this a few times, and experimented with noise removal using Audacity.
There is a small gap of "silence" at the start of the track, and a not quite similar one at the end. Listen carefully close to the end and the noise is apparent, but then goes down to zero - or close to it.
I homed in on a fraction of these two gaps - perhaps a second - maybe slightly less, and did a spectrum analysis. One shows noise at -48dB going down to -87dB out to 3kHz, while the other shows noise from -54dB going over a very similar frequency range. Interestingly both show a peak at just over 15 kHz - 81dB and -87dB respectively.
I then used the short extract from the end (before the "silence" does drop to zero) as a noise profile in Audacity, and selected the whole track for noise removal.
This does appear to remove some/most of the troublesome noise. Checking the "silent" parts again after the noise removal shows complete removal of the 15+ kHz peak, and the noise in the two gaps has now shifted down to -66dB (end "silence") and lower and -73dB (opening "silence").
To check that the levels on the samples had not changed significantly the peak around 9 minutes in was analysed, and contains a fairly wide band of frequencies up to 20 kHz decreasing from -18dB down to -90dB at over 20kHz. The levels were consistent across the versions.
It is of course possible that some of this "analysis" is influenced by other factors, such as the size of the window used for the spectrum analysis, the type of window, but on balance the measurements suggest a noise reduction of over 10dB - could be as much as 18dB - but I'm conservative. I could also have made mistakes, but I have tried hard not to. I'm willing to repeat this a few more times if needed.
Listening does suggest a clearer sound - though it may now be more important to listen in a low noise environment.
If I could find somewhere to post samples of the audio for comparison purposes, I would be willing to do so - though not the whole track. I don't know of any good sites for this purpose right now.
My concern regarding low frequency noise is partly that under some conditions I can hear it, and it is distracting, and secondly that it sometimes has a definite pitch which interferes with the intended pitches in the music. Perhaps randomly pitched noise is less of a problem.
My track was downloaded from iTunes, but the effect of the noise can clearly be heard in this track (5) - http://open.spotify.com/track/2XzLNwdooyXy2HDOrzxBub
It would also be good if others could check this out, and perhaps also find their own examples to process in a similar way. Listeners, such as JLW, would be welcome.
My opinion is that the RLPO Bridge recording does sound quite a bit better after this process, and other recordings may benefit too. That is why I started the other thread on the quality of remastering. Commercial companies should have the capability to do this kind of work, but I feel that often they don't bother to check the quality of their output. It is, after all, cheaper that way - if nobody complains.
There is a small gap of "silence" at the start of the track, and a not quite similar one at the end. Listen carefully close to the end and the noise is apparent, but then goes down to zero - or close to it.
I homed in on a fraction of these two gaps - perhaps a second - maybe slightly less, and did a spectrum analysis. One shows noise at -48dB going down to -87dB out to 3kHz, while the other shows noise from -54dB going over a very similar frequency range. Interestingly both show a peak at just over 15 kHz - 81dB and -87dB respectively.
I then used the short extract from the end (before the "silence" does drop to zero) as a noise profile in Audacity, and selected the whole track for noise removal.
This does appear to remove some/most of the troublesome noise. Checking the "silent" parts again after the noise removal shows complete removal of the 15+ kHz peak, and the noise in the two gaps has now shifted down to -66dB (end "silence") and lower and -73dB (opening "silence").
To check that the levels on the samples had not changed significantly the peak around 9 minutes in was analysed, and contains a fairly wide band of frequencies up to 20 kHz decreasing from -18dB down to -90dB at over 20kHz. The levels were consistent across the versions.
It is of course possible that some of this "analysis" is influenced by other factors, such as the size of the window used for the spectrum analysis, the type of window, but on balance the measurements suggest a noise reduction of over 10dB - could be as much as 18dB - but I'm conservative. I could also have made mistakes, but I have tried hard not to. I'm willing to repeat this a few more times if needed.
Listening does suggest a clearer sound - though it may now be more important to listen in a low noise environment.
If I could find somewhere to post samples of the audio for comparison purposes, I would be willing to do so - though not the whole track. I don't know of any good sites for this purpose right now.
My concern regarding low frequency noise is partly that under some conditions I can hear it, and it is distracting, and secondly that it sometimes has a definite pitch which interferes with the intended pitches in the music. Perhaps randomly pitched noise is less of a problem.
My track was downloaded from iTunes, but the effect of the noise can clearly be heard in this track (5) - http://open.spotify.com/track/2XzLNwdooyXy2HDOrzxBub
It would also be good if others could check this out, and perhaps also find their own examples to process in a similar way. Listeners, such as JLW, would be welcome.
My opinion is that the RLPO Bridge recording does sound quite a bit better after this process, and other recordings may benefit too. That is why I started the other thread on the quality of remastering. Commercial companies should have the capability to do this kind of work, but I feel that often they don't bother to check the quality of their output. It is, after all, cheaper that way - if nobody complains.
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