Canyon 's Collection
Grateful Dead 02/18/1971
Capitol Theater, Port Chester, NY
| Source | SBD -> Dolby A Reel -> Dolby A decode -> DAT -> Sound Forge NR -> CD-R |
| Media | audio 3 discs |
| Notes | hd1 |
| Tech Notes | SBD -> Dolby A Reel -> Dolby A decode -> DAT -> Sound Forge NR -> CD-R The Sound Forge noise reduction was used to attenuate a very narrow frequency band (in the vicinity of 8000 Hz) which was present as interference on the original reels. See my notes below for details. The original reels of the Port Chester run of '71 were audibly tainted due to a cable problem. The result is a tone which hovers around 8000 Hz with an amplitude of about +20 dB above the noise floor. This translate to a very annoying pitch, especially during quiet sections, which is in the old-tv-tube or lousy-hard-disk or maybe even the-sound-you-hear-after-you-slam-your-head-against-a-concrete-wall class of 'whine'. Because this interference is 'monochromatic' it's easy to get rid of if you have the processing power and a quick FFT algorithm. I used the filter-shaping capabilities of the Sonic Foundry Noise Reduction Plugin to tailor a very narrow notch filter which attenuated the interference without affecting the rest of the signal. And it's all done in the digital domain. Huzzah! As a side note, I actually ended up crafting many filters to process these shows. The frequency of the interference actually drifted anywhere from 7700 to 8100 Hz during a given show. This was probalby due to a slightly wandering reel speed. It made my work harder but when I tried a much wider filter I started to be able to hear the attenuation in the music. The filters generally go like this: 25 dB /- - - - - - - -\ / \ / \ 0 dB | | 7830 7900 7970 The end result is no more annoying whine! I also removed some of the nasty mic feedback in the 2/18/71 Bertha using this type of filter. Leigh Orf <orf@mailbag.com> |
| Trades Allowed | Yes |
Owned by Canyon
· Last Updated May 23, 2023
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