First live recording, some questions

[Nathan P]

I made my first live recording last night, with my Nady CM-2S and my camcorder. It turned out great, but I have a few questions. The recording was done in my church, an amazing violinist was visiting. He comes every year, he's friends with some people here. Anyway, I noticed that in the recording there is some bass that seems to be almost feeding back, but not quite, it's like there's something humming that frequency. It was probably the mic's position combined with the room acoustics. I have played around with audacity, and a bass roll off makes it sound a lot better. What is the proper procedure for doing a bass roll off, and what kind of curve should I use? I was just using the eq and rolling it off manually after 100hz, there has to be a better way to do it. Secondly, due to the heaters going and the number of people, I got some background hum. During the music it isn't really noticeable, but in some quiet parts and the speaking parts, you can hear it. I tried using the noise removal in audacity to get rid of it, but that made clapping and the speaking parts sound funny. Is there some other way to get rid of it or at least minimize it? Maybe find a different spot to choose the noise to remove or? Overall I am very happy with the recording, and I knew these two things may come up to begin with, as no live recording is going to be perfect.

Thanks,

Nathan

[greenmachine]

Whatever you do, be sure to keep a copy of the unedited original, you might change your mind later about the best way / usefulness of editing.

[Nathan P]

Whatever you do, be sure to keep a copy of the unedited original, you might change your mind later about the best way / usefulness of editing.

Of Course, I've got a copy of it on my computer, plus it's still on the tape.

Here's a sample. I'm not sure of the bitrate, I just used Audacity to encode it.

Mic_Sample1.mp3

[King Ghidora]

Some excellent violin work there for sure Nathan. And the recording sounds good to me too. The bass problems you are describing sounds a lot like what is known as a standing wave. I didn't notice it when I listened to the recording but I only listened to it once. What I know is that standing waves can play havoc with bass tones and string instruments are well known to cause problems in this area. In fact a string instrument produces opposed waves every time they are played. This is a VERY complicated phenomenon which generally shows up as a total cancellation of all bass sounds or any number of other strange artifacts in a recording. Having a bass tone rise and fall is right in line with something a standing wave might cause.

The only way to deal with this issue short of building a completely controlled enviorment designed to be perfect acoustically (very hard to do) or do what us mere mortals do - we move our mics to a different location. Standing waves are very much affected by reflective surfaces and the harder and flatter the surface the more likely it is to cause a problem. It's trial and error that shows us where to place a mic really. There's just no predicting where a standing wave might cause problems. Unfortunately if you're in a one time only situation where you don't have the opportunity to do a trial and error test you're just stuck with what you get. You might be able to reduce the effects of this problem using a good sound editor but you're just as likely to cause parts of the recording that you want to keep to be removed with the standing wave problems.

Sorry I can't give you a better way of dealing with the issue. I can give you a few suggestions. Learn your enviorment as much as possible. If you record in your church often you may be able to figure out where the sound system causes problems on a regular basis. Try to stay away from reflective surfaces like walls because standing waves often travel along such surfaces. And monitor your recording so you might be able to pick up a problem in time to move your mic during a performance. Sometimes just a slight shift of your mics position will help a lot. And if the performer does a sound check before an event be there to try to do some trial and error tests. You can record from several locations then review your recording to see where the best spot might be.

It's a very complicated problem and most people never notice it at all to be honest. You obviously have a good ear for such things because you picked it up without even knowing about their existence (I assume you didn't anyway). That gives you a leg up on preventing such problems because you have to know there is a problem before you can fix it.

[greenmachine]

What is more apparent to me in the example, are the dynamic compression artifacts. Did you use AGC (or the equivalent on a camcorder) or apply some sort of post-limiting? Does your camcorder have a manual level control? These pumping effects can make problems in the low frequency region more apparent and more difficult to correct afterwards.

[Nathan P]

I haven't had time to really play with the settings in the camera, I just plugged it in and went. I don't find the bass sound too irritating, I just notice it a little bit, it's almost as if there was a bass note that had been played in the accompaniment track that started a loop going. Sometimes it seems as if it is just part of the music. Of course, I will probably be listening to it most with headphones, and my headphones don't really pump out the bass, so I won't worry about it. I didn't notice any compression artifacts, could you point out some times and tell me what to look for? Some say ignorance is bliss, but getting good sound requires you to be able to hear the problems. I did notice when I looked at the waveform that there were some clicks(points where the waveform went to the edge of the scale), most were during the applause, but some were just randomly in the performances, but I can't really hear anything there, I can just see it. I may have noticed the standing wave because of my music background, I can always tell when a piano is the slightest bit out of tune, or when people are singing, I can hear the slightest pitchiness. It's a blessing and a curse, from one point, it is easier to determine when I sound good, whether singing or playing trombone, guitar or piano, but sometimes non professional (and some professional) singers really irritate me during performances because I can hear every single time they go off key the slightest bit.

What is more apparent to me in the example, are the dynamic compression artifacts. Did you use AGC (or the equivalent on a camcorder) or apply some sort of post-limiting? Does your camcorder have a manual level control? These pumping effects can make problems in the low frequency region more apparent and more difficult to correct afterwards.

[King Ghidora]

After listening to the clip several times it is very obvious that some sort of automatic level control is in operation. I loaded the clip into an audio editor and quickly noticed that the sound level was nearly flat even when the orchestra parts were very low or very loud. So obviously there is some AGC controlling the level on your camera. Most consumer grade cameras do have AGC. I should remember what camera you have Nathan but sometimes my memory isn't what it should be. If I remember correctly you have a GS250, right? If so then you definitely have an AGC camera. That's the same camera I have and I have come to regret not springing for the GS400 which does have manual level controls. That's the main reason I use MD for the audio portion of my projects.

I haven't noticed any problems with the bass fading in and out as you describe. I haven't listened real close so maybe I'm just missing it. I'll try to listen more carefully and see what I think might be the problem you are having.

[Nathan P]

Maybe I miss stated, I wouldn't exactly call it fading in and out, it's just certain songs had it going on, others didn't. This may be an example of one that didn't. I promised the violinist that it was for personal use only so I can't post up any full length stuff. I'll try to find some clip that have it more tomorrow. I have the Canon Elura 100, so it probably has AGC. I am looking into getting a minidisc recorder, but I'm kind of lost in the dark as coming here was the first time I've even heard of them. Any suggestions for a good low cost one I could pick up off of ebay etc. would be great.

After listening to the clip several times it is very obvious that some sort of automatic level control is in operation. I loaded the clip into an audio editor and quickly noticed that the sound level was nearly flat even when the orchestra parts were very low or very loud. So obviously there is some AGC controlling the level on your camera. Most consumer grade cameras do have AGC. I should remember what camera you have Nathan but sometimes my memory isn't what it should be. If I remember correctly you have a GS250, right? If so then you definitely have an AGC camera. That's the same camera I have and I have come to regret not springing for the GS400 which does have manual level controls. That's the main reason I use MD for the audio portion of my projects.

I haven't noticed any problems with the bass fading in and out as you describe. I haven't listened real close so maybe I'm just missing it. I'll try to listen more carefully and see what I think might be the problem you are having.

[greenmachine]

The NH700 (or NHF800, similar unit with radio remote) offers all the recording features you need at an affordable price. I use one myself and am very happy with the results. This question appears pretty frequently here in the forums, so you may want to take a look around for details / other recommendations.

[greenmachine]

Nathan, I've prepared a few samples* for you to demonstrate the effects of dynamic compression so you can listen/see/judge for yourself. It's pretty hard for me to describe compression artifacts. I would describe it as some kind of "ducking" when a sudden peak arises, particularly noticeable in drum tracks. It can sound very unnatural when overdone.

First, an acoustic guitar solo uncompressed:

guitar.mp3

Then applied some compression to it:

guitar_c.mp3

Here's another sample of a trio (piano, el. bass, drums), first with all their natural dynamics:

trio.mp3

Again, applied some (too much) compression:

trio_c.mp3

See also here:

http://en.wikipedia.org/wiki/Dynamic_compression

and here:

http://en.wikipedia.org/wiki/Automatic_gain_control

*Samples created with Magix Music Maker, compression and graphs by Adobe Audition, pictures edited with Irfan View, mp3 compression by lamedropXPd

Edited February 7, 2007 by greenmachine

[Nathan P]

Yup, It was more apparent to me on the second clip, I head some clicks, almost as if it was pausing for a split second right after the louder part started. I stopped listening cause I've got to get to school, but yeah, thanks for the examples.

Nathan, I've prepared a few samples* for you to demonstrate the effects of dynamic compression so you can listen/see/judge for yourself. It's pretty hard for me to describe compression artifacts. I would describe it as some kind of "ducking" when a sudden peak arises, particularly noticeable in drum tracks. It can sound very unnatural when overdone.

First, an acoustic guitar solo uncompressed:

lowgainFXtest_normalized.mp3

Then applied some compression to it:

lowgainFXtest_normalized_filtered.mp3

Here's another sample of a trio (piano, el. bass, drums), first with all their natural dynamics:

DR000032.mp3

Again, applied some (too much) compression:

DR000033.wav

See also here:

http://en.wikipedia.org/wiki/Dynamic_compression

and here:

http://en.wikipedia.org/wiki/Automatic_gain_control

*Samples created with Magix Music Maker, compression and graphs by Adobe Audition, pictures edited with Irfan View, mp3 compression by lamedropXPd

[rayzray]

[edit]

Edited February 12, 2007 by rayzray

[King Ghidora]

I also use a NHF800 Nathan. All HIMD recorders will have the same sound quality so unless you want the new features there's really no reason to buy a newer model. Personally I like the fact you can use AA batteries with the first generation models (the two mentioned by greenmachine). Newer models use a gumstick battery though some can use AA batteries with an add on battery module.

You should be able to get a first gen HIMD for around $125 if you check the right places. There's a place out of California that sells them for that price. I can give you a link to them if you want it.

[A440]

first gen HIMD for around $125 if you check the right places. There's a place out of California that sells them for that price. I can give you a link to them.

King G., I've already got too many MDs, but I'd like to know about that link.

greenmachine, thank you so much for making these clips. They make clear what compression and AGC do.

Nathan, I also use the NHF800 and it is one tough, reliable little gadget. The NH700 is exactly the same unit with a different remote, and I never bother with the FM radio, so you might as well get the NH700. (I got one a year and a half ago as a backup and I've never had to use it because the NHF800 has survived all my abuse.)

I indulged myself and got the RH1 to upload all my old MDs. But I'm still using the NHF800 regularly, and keeping the RH1 mostly for playback (Dynamic normalizer has its uses) and uploading. When I want to be ultra stealthy I bring the RH1, but I don't think the price difference is worth it unless you need to upload old MDs. And like greenmachine and others, I very much appreciate being able to use the AA battery in the NH700 and NHF800.

[King Ghidora]

I seem to only be able to find the email address for the place that quoted me that price A440. I'll send it to you in a PM so I won't feed any spam bot crawlers.