Rockbox Technical Forums

Support and General Use => Recording => Topic started by: _tunic_ on May 03, 2007, 09:22:17 AM

Title: Seeking help to improve recording concerts with iRiver H320 (Gain control)
Post by: _tunic_ on May 03, 2007, 09:22:17 AM
Hi Rockbox people!

I recently bought an iRiver H320 on eBay, and added some GM Standard microphones (with battery box, see http://www.geocities.com/greenmachine_audio/de-over.html ). It turns out that they make a pretty good pair, or a threesome even :-)

I've been taping three shows now. Two of them turned out very good, the third one not so but that was mainly due to the bad soundquality of the venue itself, or perhaps that I was standing to close to the drumkit. Not sure if I'm allowed to name names here so I won't but if you have access to dimeadozen.org feel free to grab them for a listen, the nickname there is the same as here. I've uploaded the first recording already, the others will be posted in the weekend probably, and some more next week (doing 6 shows in 8 days of my favourite two bands). Some of the shows will be up on the archive.org as well (the one band is on it, the other not).

Sorry if this is getting too long of a story.... The main flaw in all recordings is that the volume is pretty low. I've attached an image of how the last recording looks in audacity. Most of the real loud parts is the applause actually. So I just want to check that I haven't messed up the Rockbox settings. I'm using a mainline build (r13027-070405), the recording settings are the following:
- Format: PCM Wave
- Frequency: 44.1kHz
- Source: line-in
- Channels: stereo
- file splitting disabled
- prerecord time disabled
- clipping light: main unit (I don't think it has ever blinked yet)
- trigger: off
- Automatic Gain Control: Live (slow)
- AGC clip time: 400ms

And in the recording screen it mentions:
- Gain left: -0.5dB
- Gain right: -0.5 dB
- AGC: live (slow) 48.5 dB

My main concern is that I have the gain settings set incorrectly, as I don't really know what it means. The manual doesn't really explain it in that much detail, so I would love some more detailed explanation of this feature.
I'm really a noob when it comes to taping.

I've been playing around with the recording levels. The first two shows it was set way too low (-50dB and -40dB), I was scared of setting it too high and thereby distorting the mics. Last night it was at 0dB, but it turned out still a bit too quiet (see the image). I was sitting on the balcony though of a pretty large venue. It could also be the microphone, as it's really small (and cheap), but the quality is great, very clean.

I've also been reading the thread on the Recording Enhancements Pack (not all 50 pages, but the first and the last two/three). Would love to try it out, but judging from the last pages it isn't really stable at the moment so I'll rather wait until it's pretty much bugless.

Thanks in advance for any tips you guys can give me, and also big thanks to all the developers who have spent their free time in creating Rockbox!

Will be taping the next show in about 4 hours, so any fast help is very welcome  ;D


edit:
- don't feel offended by that last remark, tomorrow is fine too ;-)
- one remark about the added picture: the actual show started after 10 minutes, wheer i drew the line

[attachment deleted by admin for age]
Title: Re: Seeking help to improve recording concerts with iRiver H320 (Gain control)
Post by: petur on May 03, 2007, 10:48:25 AM

- Format: PCM Wave
- Frequency: 44.1kHz
- Source: line-in
- Channels: stereo
- file splitting disabled
- prerecord time disabled
- clipping light: main unit (I don't think it has ever blinked yet)
- trigger: off
- Automatic Gain Control: Live (slow)
- AGC clip time: 400ms

And in the recording screen it mentions:
- Gain left: -0.5dB
- Gain right: -0.5 dB
- AGC: live (slow) 48.5 dB

1) use AGC only in safety mode
2) set your h320 gain to around +10.0 dB (or 15 if you're unsure about expected soundlevel)
3) during the concert AGC safety will lower the gain if needed. Having a pre-amp i.s.o. a battery box helps more in getting the gain right. If you end up at -0.5dB at the end of the show you were lucky, you hit the bottom gain margin (anything louder starts clipping)



I've been playing around with the recording levels. The first two shows it was set way too low (-50dB and -40dB), I was scared of setting it too high and thereby distorting the mics. Last night it was at 0dB, but it turned out still a bit too quiet (see the image). I was sitting on the balcony though of a pretty large venue. It could also be the microphone, as it's really small (and cheap), but the quality is great, very clean.

don't use negative gains, the input circuit will clip anyway on anything below -3 to -5 dB
maybe get better mics, a pre-amp and a good system to mount the mics (mic position and direction is important). See http://www.taperssection.com and check out the gear that chris church sells: good quality for an ok price. His st-9100 with cardoid mics are highly recommended ;)


I've also been reading the thread on the Recording Enhancements Pack (not all 50 pages, but the first and the last two/three). Would love to try it out, but judging from the last pages it isn't really stable at the moment so I'll rather wait until it's pretty much bugless.

You don't need the REP unless you want eye-candy and some other features that aren't key to recording.

My recordings are also always with a safe margin below max. In audacity, use the hard limiter (the one you need to install extra as part of the filter kit), and set that to lower the applause noise, after that you can up the gain...

Don't use any other AGC setting than safety, and try to get the gain right as much as possible, this will give you equal gain over the whole recording.

It is quite normal you need several shows to get the recordings ok, and remember, mic placement is important.

have fun!
Title: Re: Seeking help to improve recording concerts with iRiver H320 (Gain control)
Post by: _tunic_ on May 03, 2007, 11:35:09 AM
thanks a lot petur! I expect the volume to be louder tonight (same band as yesterday, but smaller venue and I want to stand closer to the stage), so I set the gain to +15 to be safe, and AGC to safety (it now says 33dB)
Will know in a couple of hours what the difference will be.

Quote
It is quite normal you need several shows to get the recordings ok, and remember, mic placement is important.
yeah I know. Perhaps i should have recorded some bands first that I don't like as much. But I'm already quite happy the way it came out so far. Especially since I had no clue what half of the settings are for  ::)
I have the mics currently hung over my tshirt collar if I'm standing, definitely not the best place but I don't have clips, don't want to wear (sun/fake?) glasses or a cap.

If anyone could still explain what gain does in more detail or point me to where there is a basic explanation. I do understand most of what petur just told me, but to be able to find out the right levels, I should first get to know the terminology properly.
Title: Re: Seeking help to improve recording concerts with iRiver H320 (Gain control)
Post by: nigelsh on May 03, 2007, 09:24:33 PM
In audacity, use the hard limiter (the one you need to install extra as part of the filter kit), and set that to lower the applause noise, after that you can up the gain...


Sorry to get a bit off topic but do you have some instructions on how to use the hard limiter?

Thanks
Title: Re: Seeking help to improve recording concerts with iRiver H320 (Gain control)
Post by: petur on May 04, 2007, 02:29:07 AM
from the audacityteam.org wiki:

Quote

The Hard Limiter controls are:

dB limit: the input signal level above which the input signal will be clipped.

Wet level: controls the amount of the clipped signal fed to the output. It thus acts as a volume control applied after the limiter (just as if you applied the effect and then used the Amplify effect).

Residue level: controls the amount of the clipped signal that will be mixed back in. By default the value is set to zero and so the clipped signal is discarded. By raising this level, some of the clipped signal will be restored, making the limit softer and retaining more of the peaks and troughs of the original waveform. Alternatively if you turn the residue full up and the Wet signal full down, you get only the pieces of waveform that are above the dB limit you chose.


or:
first value is the limit: set it above the music and below the noise you want to lower
second value: set to 1 or max
third value: I set that to 0.5 I think
Title: Thanks so much!
Post by: _tunic_ on May 04, 2007, 03:05:48 AM
Hi,

here's an update. Your tips made a big improvement already petur, thanks again! The opening act turned out better than the main act, but i guess that's mainly due to the sound quality in the hall. I've added a screenhot again (from the opener), looks just perfect to me. Will have to use the click removal feature of audacity to remove some plops. Had the mics hang over the balcony, and I moved them around a bit during the recording. That's another lesson learned.

cheers,
_tunic_

[attachment deleted by admin for age]
Title: Re: Seeking help to improve recording concerts with iRiver H320 (Gain control)
Post by: petur on May 04, 2007, 05:00:30 AM
for that little amount of peaks I usually zoom in on them and do a custom hardlimiter on them to get them below the rest of the recording, then you can up the overall gain.

Are your mics omnis or cardoids (directional). I'd look for some way to mount them and not hang them somewhere.

I've made myself a mini micstand made out of 30cm of thick (5mm^2 or more) electrical wire. The wire is so thick it keeps the position you bend it in, so I can form it to point to anything. On one side I stripped the insulation and grouped the wires so that I can clip my (cardoid) mics on them and point them in a nice 90 degree angle.

As I said, mic placement is important ;)
Title: Re: Seeking help to improve recording concerts with iRiver H320 (Gain control)
Post by: redwood on May 07, 2007, 08:14:05 AM
_tunic_  -

You recorded Dexter Romweber of the Flat Duo Jets? Very cool. How was the show?
Title: Re: Seeking help to improve recording concerts with iRiver H320 (Gain control)
Post by: _tunic_ on May 07, 2007, 10:13:18 AM

_tunic_  -

You recorded Dexter Romweber of the Flat Duo Jets? Very cool. How was the show?
Yeah I did, he's been opening for Cat Power on her tour. If I would not have been such a big Cat Power fan I would have said that I liked Dexter way better. It's just him on guitar/vocals and his sister Sarah on drums, well at least that's how he introduced her. I had never heard of him, but I'm glad I decided to tape him. It's like the parents of the White Stripes playing old 1950's Rock'nRoll jukebox tunes. Liked it a lot, even though it's not really my style of music. And my recording from Eindhoven sounds great.

Thanks again petur for all the help, I've been having so much fun this week! I'm now off to the last one  :'(
My mics are cardoids I think, perhaps omnis would have been a better choice as I like to hang them over the balcony so I don't have them stuck on my body. But they have a very nice sound quality.

The recordings of Low will be up on Archive.org some time later this week if I have enough time ( http://www.archive.org/search.php?query=collection%3ALowMusic )