Shaving Fish -- Audacity is you Friend
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Bronze Member Username: Steve542England Post Number: 16 Registered: Aug-05 | Shaving Fish -- Audacity is you Friend OK, this is using Audacity version 1.2.2 (... suspect newer version now out -- see http://audacity.sourceforge.net/) to fix a problem sent me by James Hicks (see posts https://www.ecoustics.com/electronics/forum/home-audio/160425.html). James is running into an awful drone when recording from LP and has sent me a sample to play with. Fortunately, fixing this one turn out dead easy  OK let's look at the problem. Fire up Audacity and load the sample, from "Shaved Fish" by John Lennon. See Pic 1. Here I have fiddled with the timescale to take a close look at the signal -- and have also magnified the vertical (to do stuff like this, see the Tips section at the end). Left channel is at the top. Now.. we are looking at the silent lead-in at the start of the track! OMG - this should be a flat line! L and R channels quite different. L (top) has compounded of several frequencies. Counting 10 of just the smallest cycles and checking the time (in mins:secs at bottom of picture) and fiddling with a calculator we find that these are at 181.8 Hz so will be very audible. Looks like James is in a country with 60Hz power -- and the generators are running a tad fast as 3 x 60 => 180 Hz Can also see some sort of sub-harmonic of 181.8 -- expect it's the 60Hz base tone but not going to go further for now; sub and super harmonics are usual (I'm in the UK with a 50Hz mains, so I see multiples of 50 not 60). Over on the R channel (bottom, see Pic 2) and peak counting 15 cycles this time I see that the signal is 10.8 Hz. That's in the region of turntable rumble. There is also a slow beat (the 10 Hz increases/decreases cyclically) which could be anything from the record pressing to the 33 1/3 rotational speed to whatever. Interesting that there is NO 60 / 181 Hz signal! That's probably due to screening issues on the phono wiring or some other electronics oddity; perhaps the L channel lead is getting close to a power chord inside the case -- but the R does not. So to fix this. As I'm going to use different methods, I'll split the stereo signal into 2 mono's. We can recombine again at the end. To do this, use the pull-down arrow next the label, top of the waveform box to the side of the title. Use the option "Split Stero Track". Fixing the Left channel ================= OK. On the Left I'm going to use Audacity's noise removal option to take out the 60 / 180 Hz tones. This is a bit of a hammer -- so a very light touch is needed. How noise removal works: a) first analyse what the "noise" is made of b) then do some horrible maths on the whole signal, essentially gutting it into all frequency components then reassembling it LESS the things found it a). It can go wrong and leave out too much (create bad sounding "artifacts") - so it tries to help by only taking away the amount found in the noise -- after all, some signal like that could have been part of the music. To help manage this, Noise Removal comes with a slider to adjust the strength of the effect. So on the Left channel, in the track run-in where there is just "drone" and no music, select a nice drony piece a second or two long. This will be the noise sample used in a). Do this by swiping the wanted part of the signal on the L channel only. On the top menu options there is "Effect". Under this is "Noise Removal". Select that, then click on the Button "Get Noise Profile". Back to the signal window. Click in the left edge of the Left channels info box; this selects the whole of the L signal. Now to remove that pesky drone. Using Effect > Noise Removal... Step 2. Set the control slider all the way to the left or perhaps 1 notch in, so to have Less effect and click OK. This is the heavy number crunch bit and might take some time. It finishes and... The drone signal should now be gone. See L of Pic 3. NB you can always hit Ctrl-Z to Undo. Fixing the Right channel ================= Here a different method will be used. Select the whole R channel by clicking in the info box to the left side of the signal. We'll use a simple filter to dump all the LF stuff (purists shudder!!). Effect > Hi-Pass Filter and set the cutoff frequency quite low; say 45 Hz. That means signal ABOVE 45 Hz will be left alone; stuff below 45Hz will be attenuated (reduced). It won't go completely. Click OK and it does it's thing. Why didn't we do this for the Left channel?? Because we'd loose lots of interesting music below 180Hz. Finishing Up ========= Combine the signals back to Stereo. On Left channel, click options arrow to right of the title. Select Combine Stero Track.. and the tracks come together It's a bit quiet, so we can normalise it (make it a standard volume). Select whole track (click in info box on left) and then click on Effect > Normalise and hit OK. Sounds good, eh? Let's Save our Work! File > Export as Wav, Export as MP3, Export as Ogg Vorbis The Cut selected track command (to remover long silences), fade-in / fade-out are also useful. There is much much more that Audacity can do over & above what is described here. Play with it! Other comments: This is sampled at 44,100 per second. Recording at a higher sample rate would sound subtly better but will increase file sizes. I use at least 96K for my recordings. OGG files sound better then MP3 and give smaller files for the same quality. BUT not all players work to playback .ogg files. .WAV and FLAC files are best -- but file sizes are huge. Audacity Newbie Tips ================ To hear -- press Space bar. Another Space bar stops. To hear from beginning -- hit Home key then Space bar. To increase / reduce timescale click on the + or - magnify glass button To increase amplitude click left mouse button or right mouse button when the pointer is over the vertical sale (just to right edge of the info box) To select music -- swipe it with click-and-hold on the mouse, just like on a wordprocessor. To adjust edges of the swipe, hover the mouse near the edge and a small hand is shown. Click and hold; moving the mouse now moves the highlight edge slightly. You can control the quality settings under File > Preferences (look around). Note you must close & restart Audacity for these to take effect. Whew! Steve PS having trouble posting the pics and before/after samples; will put some links in to this in the next post. |
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Bronze Member Username: Steve542England Post Number: 17 Registered: Aug-05 | Had to put thee on my own site... Pics and samples: Before sounds like: and After sounds like: You'll need an ogg player for these; see http://www.tucows.com/preview/336595 or http://www.mediamonkey.com/download.htm Hm. Though this works, it does take some effort. Think might be worth carefully checking around the pickup wiring, arm, (inside the turntable if possible) and the phono leads to make sure that it does not stray near a power chord. Also check that the earthing screws are not corroded & are making good contact. Take care with this!! Bye, Steve |
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New member Username: GonetomorrowLexington, KY US Post Number: 4 Registered: Sep-05 | A plethora of thanks to you Steve. The cleaned-up track sounds superb. Thank you for your detailed step-by-step, I shall reference it for my future recordings (I just picked up a 10-LP boxed set of Toscanini conducting all 9 of Beethoven's symphonies, next project!). I have discovered a few oddities with my turntable-to-PC setup, the electrical oddities you mentioned not withstanding. I did some more investigating into to the cause of the drone. I took to a local record shop, where a friend of mine was kind enough to let me test it on different receivers and amps. It worked and sounded excellent, no drone whatsoever, even when I tested it at the shop with my little phono pre-amp. According to Dave the turntable/LP expert who owns the shop, he said to me that Pioneer players, mine in particular (PL-115D), in his experience never develop a drone, as they have a reputation for extreme reliability. This was apparenty so after we tested it at the shop. So, the problem is with my PC setup apparently, or some electrical oddity which Steve mentioned. I tried grounding the turntable to an electrical socket plate's center screw, but that only made an even louder noise. I re-grounded the wire to the amp's grouding screw, but this time there was NO DRONE AT ALL. Even with the volume pegged. I fiddled with the wire to see if I could reproduce the drone, and apparently, the drone does not occur if the grounding wire is connected coming down perpendicularly to desk. If it is connected from either side (as I was wont to do), then a dorne is produced. So, I have no idea why the position of the wire matters so much in my case, but Im so glad the drone is gone, that is moot to me now. Thanks for your help Steve, I'm sure the drone will reutrn someday, but I'll be able to deal with it. James Hicks (US) |
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