Rockbox Technical Forums

Support and General Use => Recording => Topic started by: blindhippie on January 29, 2007, 11:23:31 PM

Title: Tips on recording for a newbie
Post by: blindhippie on January 29, 2007, 11:23:31 PM
I am trying to get into live music recording and i am using my iRiver with RockBox and REP. I recorded my first show and have a little problem. I am a total techno-retard, as you will see, so bear with me.

I used the "Live" AGC setting, and i was under the impression that it would adjust the gain to the correct level "automataically," so i didn't make any changes to the initial gain settings, which were somwhere around 0. I was seeing the meters work, so i figured all was fine. I didn't realize how slow the gain would increase, so now my recording gets gradually louder, eventually reaching the optimum level after about 20 minutes.

Questions:
What should I set the gain for to start out if i am recording a moderately loud rock show?

How can you tell what the peak meters are reaching? There are no numbers on the meters.

How do i know what dB level to set the clipping limit for?

Finally, and this is non-RockBox related, but if anyone could help it would be great, is there any way i can correct this using Sound Forge? I have that but don't really know how to use it for something like that and i couldn't find any support for it. I think the Graphic Dynamics effect is what i want, but i can't figure out the settings (threshold, ratio, attack, release). anybody know where there is a good explanation of that?

Sorry. I probably got no business with this stuff. I can't understand half of what you guys are talking about in these forums.
Title: Re: Tips on recording for a newbie
Post by: petur on January 30, 2007, 04:27:07 AM

I am trying to get into live music recording and i am using my iRiver with RockBox and REP. I recorded my first show and have a little problem. I am a total techno-retard, as you will see, so bear with me.


No problem, at least you got the equipment and firmware right ;) But a lot more depends on what microphones you use...


I used the "Live" AGC setting, and i was under the impression that it would adjust the gain to the correct level "automataically," so i didn't make any changes to the initial gain settings, which were somwhere around 0. I was seeing the meters work, so i figured all was fine. I didn't realize how slow the gain would increase, so now my recording gets gradually louder, eventually reaching the optimum level after about 20 minutes.

Most live show tapers don't use the AGC except in its Safety mode


What should I set the gain for to start out if i am recording a moderately loud rock show?

I mostly set it to +15dB and enable AGC Safety... At the end of the show it ends up at around +5dB to +8dB but that's just experience: get to know your mics and gear, don't expect the first show to be perfect. And always go on the safe side!


How can you tell what the peak meters are reaching? There are no numbers on the meters.

How do i know what dB level to set the clipping limit for?

The scale can be configured, default has 0dB on the right side so if it reaches that it will clip.
The cliplight will activate on 0dB I think, hence 'cliplight'


Finally, and this is non-RockBox related, but if anyone could help it would be great, is there any way i can correct this using Sound Forge? I have that but don't really know how to use it for something like that and i couldn't find any support for it. I think the Graphic Dynamics effect is what i want, but i can't figure out the settings (threshold, ratio, attack, release). anybody know where there is a good explanation of that?

I haven't fiddeled with dynamic range compression because I can't find a setting that sounds ok for me.

I can recommend reading around at http://www.taperssection.com (registration required) for mor info on recording. Get good mics and, for rock concerts, a battery box or mic amp. It did wonders for me.
Title: Re: Tips on recording for a newbie
Post by: blindhippie on January 30, 2007, 09:27:35 AM
Thanks, Petur. I have mics (AKG 300s), a pre-amp, and battery pack that a friend has loaned me (he has another rig, so i think he'll let me keep this one for a while, especially if i send him some good shows). I was able to select sections of the recording and adjust the gain using the Dynamics effect. you can boost the output along a line so that the increase is greater at certain levels to match what you are looking for. I' m not sure how it sounds, though. gotta test it some today. I think my next effort will come out much better, now that i have read the manual and some of the posts. :D
Title: Re: Tips on recording for a newbie
Post by: petur on January 30, 2007, 10:52:57 AM
nice to hear... sounds like you've got the stuff you need :)

Set the gain of the pre-amp so that your signal reaches around 0dB with the gain on your iriver set to 10dB, that gives you 10dB headroom the AGC-safety can use.

If in doubt, set the gain safe enough and boost it in an editor later. Better a little hiss as distortion.

just my thoughts as amateur recorder ;)
Title: Re: Tips on recording for a newbie
Post by: westkc3 on January 30, 2007, 11:07:08 AM
Try normalizing the file before splitting the tracks.  

Normalization raises or lowers the overall amplitude or loudness level of a sound file to a selected point, generally up to where the loudest amplitude peak in the file rests just below the 0dB clipping level The clipping level is the cut-off point where the audio signal information can be accurately digitized.
Title: Re: Tips on recording for a newbie
Post by: blindhippie on January 30, 2007, 10:38:31 PM
Quote
Try normalizing the file before splitting the tracks.


I did that already. But since the second half of the show is at the right level, it didn't change the beginning much.

Quote
Set the gain of the pre-amp so that your signal reaches around 0dB with the gain on your iriver set to 10dB, that gives you 10dB headroom the AGC-safety can use.


So I set the pre-amp gain so that the meters are at the clipping point and then set the iRiver gain to +10dB and that *lowers* the levels to allow 10dB headroom? That sounds backward (but everything seems backward when 0 is loudest volume).

Thanks for such quick responses btw. y'all rock! (that's how we say it down here in Atlanta).
Title: Re: Tips on recording for a newbie
Post by: whatboutbob on January 31, 2007, 03:40:08 AM
That's not quite what petur meant.

He means set the iriver to +10dB, then adjust your preamp so that levels are about 0dB (though I would suggest setting it just a tad lower than that - maybe -3 or -5dB).  So the combination of gains from the iriver pre and the external pre take it up to around 0dB.

That way, using safety AGC, if the gig is louder than anticipated the AGC has 10dB headroom to decrease the gain if need be, so that you don't get distortion.

As far as salvaging the existing recording - 'tis a good lesson on why to stay away from AGC if possible (the only time i use agc is in a situation where i know I won't be able to check levels - i set safety agc just in case I've set the levels too high).

Its going to be a pain in the arse to bring the levels back up.  The only time I've had to do this was when I adjusted levels manually in the middle of a set.  I knew how much gain I'd applied so I simpy normalised the "pre-gain" quiet section by that amount , then did a crossfade between the two.  Took a bit of fiddling. Would hate to have to do this over multiple incremental gain increases, but as far as I can see that's what you'd have to do.
Title: Re: Tips on recording for a newbie
Post by: petur on January 31, 2007, 03:47:43 AM
sorry for being so confusing ;)

what I wanted to say:

I try to set my pre-amp gain so that during a concert, my levels are just below 0dB (ie max level) with the iriver gain set to +10dB (or +15dB for even more safety)

This way, if the concert somehow gets louder than expected, I still have 10dB margin.

Getting the levels right is something to be done during the first concert, after that just remember how the pre-amp was set.

I see whatboutbob got before me but I'll post this anyway :p
Title: Re: Tips on recording for a newbie
Post by: petur on January 31, 2007, 03:48:52 AM

As far as salvaging the existing recording - 'tis a good lesson on why to stay away from AGC if possible (the only time i use agc is in a situation where i know I won't be able to check levels - i set safety agc just in case I've set the levels too high).

Its going to be a pain in the arse to bring the levels back up.  The only time I've had to do this was when I adjusted levels manually in the middle of a set.  I knew how much gain I'd applied so I simpy normalised the "pre-gain" quiet section by that amount , then did a crossfade between the two.  Took a bit of fiddling. Would hate to have to do this over multiple incremental gain increases, but as far as I can see that's what you'd have to do.


One tip is to use audacity's envelope tool to gradually change gain over time.
Title: Re: Tips on recording for a newbie
Post by: blindhippie on January 31, 2007, 09:11:23 AM
Thanks, that makes sense now. I am going to try to normalize the individual songs and see how that works. I'll look into Audacity, too.
Title: Re: Tips on recording for a newbie
Post by: petur on January 31, 2007, 11:47:21 AM
hmmm... I don't think normalizing individual songs is the way to go if you still want to listen to the concert as a whole....

Check the envelope tool of audacity, it allows you to gradually change gain, which is what you want to compensate the AGC
Title: Re: Tips on recording for a newbie
Post by: virelai on January 31, 2007, 05:15:00 PM
Hy i'm an iriver ihp120-rockbox user too, and, the recording feature is the one i use the most, as i record daily university lesson (didn't have the occasion to try it on a live gig).

So,as i cannot check my input levels all the time, i have to set one input level at the beginning, and activate AGC. Till now i've only tried the "voice" agc mode as it is the faster, and because i usually set gain to nearly the maximum ( about 46 db). At this point my first question is:
Does the latest iriver hp120 firmware only allows input levels up to around 24 dbs (i'm using a december 06 firmware version)? And if yes, why the maximum input levels where lowered?
I have to point out that i'm just using the mic that came with the iriver, that i'm recording to mp3 format at 56 Kbps mono, so my goal here is not quality, but just avoid clipping, without being forced to keep my eyes on the peak meters.

Second question is: what kind of pre-amp gear are you using guys? Does it do the job? and, does the rockbox peak meter on the iriver take into account the pre-amp gain boosting (yes, i know,this is al really stupid question  ;D )?

Third and last one: can any of you explain how the triggering thing works? Does it help somehow to avoid clipping? I had a hard time finding an explenation on the site,as the one in the manual is actually unavailable.

Thanks in advantage and bye! :)
Title: Re: Tips on recording for a newbie
Post by: petur on January 31, 2007, 05:51:06 PM

Does the latest iriver hp120 firmware only allows input levels up to around 24 dbs (i'm using a december 06 firmware version)? And if yes, why the maximum input levels where lowered?
I have to point out that i'm just using the mic that came with the iriver, that i'm recording to mp3 format at 56 Kbps mono, so my goal here is not quality, but just avoid clipping, without being forced to keep my eyes on the peak meters.

Second question is: what kind of pre-amp gear are you using guys? Does it do the job? and, does the rockbox peak meter on the iriver take into account the pre-amp gain boosting (yes, i know,this is al really stupid question  ;D )?

Third and last one: can any of you explain how the triggering thing works? Does it help somehow to avoid clipping? I had a hard time finding an explenation on the site,as the one in the manual is actually unavailable.


1) rockbox enables the maximum gain range the hardware provides (unless a bug got in there) - my h340 (which has the same ADC as yours) goes up to +48dB

2) I've got myself a preamp based on quality specs, not gain levels, so no help there. You could also try to find a more sensitive directional mic. The peakmeters show the levels of the digital signal, after pre-amp and iriver gain.

3) triggering is for pausing and resuming recording based on levels, so only record if there's something to record, not the silent parts. May be of use to you...
Title: Re: Tips on recording for a newbie
Post by: virelai on January 31, 2007, 06:42:32 PM
wow, that was so fast! thank you!

but, there's something i didn't get:

Quote
I've got myself a preamp based on quality specs, not gain levels, so no help there


i'm sorry, but, what you mean with "based on quality, not gain levels" ?   :-[

thank you
Title: Re: Tips on recording for a newbie
Post by: petur on February 01, 2007, 03:21:39 AM

Quote
I've got myself a preamp based on quality specs, not gain levels, so no help there


i'm sorry, but, what you mean with "based on quality, not gain levels" ?   :-[

I got a pre-amp that doesn't add so many extra dB gain as I don't need it (into rockconcerts too), but I looked more at the quality side of things (frequency response, distortion, noise floor, ...)

For your purpose (low quality voice recording) you'll probably have to look for a more sensitive mic and/or a pre-amp that has enough gain.

That's why I said I couldn't help you with a pre-amp, we have different targets to meet ;)
Title: Re: Tips on recording for a newbie
Post by: virelai on February 01, 2007, 09:48:41 AM
Thank you.

I'm wondering...is it a "normal size" pre-amp, or is it somehow portable? I mean, how do you handle it on a live show, if what you're using is a standard size pre-amp (like the studio, or even home ones), isn't it too cumbersome? and,what about the alimentation?
Title: Re: Tips on recording for a newbie
Post by: Zeke on February 01, 2007, 10:31:57 PM
Howdy All:

There's an awesome amount of taping info at http://www.taperssection.com/

It was there that I first heard about rockbox.  Tons of good recording information, and more minutae regarding preamps than you'll believe.

Many people get away with a pair of good mics and a battery box.  A battery box powers the microphone (with a higher voltage than your H120 can provide) which yields a stronger signal which is more resistant to distortion.  The one I have allows you to set the bass cutoff freq which can be a big help recording a show with booming bass.

I haven't recorded yet with my H140, but hope to soon.  I have recorded some shows with laptop and quality soundcard and my mic rig though --  the battery box makes a world of difference.

Rock on,

Zeke