Rockbox Technical Forums

Support and General Use => Recording => Topic started by: amoergosum on December 06, 2006, 12:26:22 PM

Title: *RB recording in a quiet environment*
Post by: amoergosum on December 06, 2006, 12:26:22 PM
Hello,
this problem doesn't have anything to do with my
external Sony mic. It has to do with Rockbox.
When I want to record in a quiet environment I obviously
set the gain up to the max. Now here's the problem:
Of course there has to be a natural constant hissing
sound which occurs naturally if you record quiet sources with
the gain set at the max.
But with the Rockbox firmware the hissing sound rises each time
the audio signal occurs.
With the Iriver firmware that's not the case.
Could anyone solve this problem?
That would be a big christmas present for sure...
best,
Ben
Title: Re: *RB recording in a quiet environment*
Post by: Davide-NYC on December 06, 2006, 01:13:55 PM
Is AGC set to OFF?
AGC = Automatic Gain Control.

I record all the time (daily) and I am pretty sure there is nothing (major) wrong with RB recording.
Title: Re: *RB recording in a quiet environment*
Post by: Febs on December 06, 2006, 01:42:54 PM
But with the Rockbox firmware the hissing sound rises each time
the audio signal occurs.

Does this hiss increase when audio occurs or when there is silence?  I agree with David that the AGC is most likely the culprit, although with AGC I would expect the hiss to rise when the audio signal is low and diminish when it is high.

(Unless the recording function has a noise gate feature that I'm not aware of ...)
Title: Re: *RB recording in a quiet environment*
Post by: Llorean on December 06, 2006, 03:20:20 PM
Another question: What format, bitrate, and frequency are you recording at? It'd be helpful to make sure you're testing with uncompressed WAV first, because otherwise the hiss could just be compression artifacts relating to the codec, or something like that.
Title: Re: *RB recording in a quiet environment*
Post by: petur on December 06, 2006, 04:22:32 PM
apart from the above, I can only recommend a good mic and an external mic amplifier
Title: Re: *RB recording in a quiet environment*
Post by: amoergosum on December 06, 2006, 04:43:40 PM
First of all…I use a really good Mic.
It’s a Sony ECM-MS907.
Ok….here’s a short sample I just recorded…so you can hear what I’m talking about.
Link:   http://z33.zupload.com/download.php?file=getfile&filepath=11243


The hissing sound doesn’t have anything to do with compression
artefacts.
I recorded at 192kb/s (MP3), with maximum gain: 40.5 dB.
AGC is always switched off so the problem is not related with that.
As you can hear the hiss increases when audio occurs.
(in my sample you can hear it really well when I hit the higher notes
on the piano).

/Ben

Title: Re: *RB recording in a quiet environment*
Post by: mlind on December 06, 2006, 04:45:52 PM
If you are recording mp3 and the hiss comes together with the signal, then it sounds like a problem a friend of mine had with an earlier build. The sound was "gated" in some way.
(I never listened to it, only heard his description)

If so: Update to the latest version of RockBox and try again
Title: Re: *RB recording in a quiet environment*
Post by: amoergosum on December 06, 2006, 05:12:16 PM
If you are recording mp3 and the hiss comes together with the signal, then it sounds like a problem a friend of mine had with an earlier build. The sound was "gated" in some way.
(I never listened to it, only heard his description)

If so: Update to the latest version of RockBox and try again


well...I'm using a built of "Mmmm" which is maybe 2 or 3 months old.
Maybe I should try a new one.




Now this is interesting…: (tried with my older built)

I just recorded two almost identical samples…
The only difference was the quality.
1)   192 kb/s
2)   wave

The hiss-when-audio-occurs is really strong with mp3-recording.
With wave quality it’s only the natural constant hiss.
So it must have something to do with the codec.
Title: Re: *RB recording in a quiet environment*
Post by: amoergosum on December 06, 2006, 06:06:01 PM
I just tried out the built which one can find in Mmmm's signature.
Well...now I can't find the mp3 codecs anymore.
There are only three options>>>
1)PCM Wave
2)WavPack
3)MPEG Layer 3

where is the mp3 option?
Title: Re: *RB recording in a quiet environment*
Post by: Febs on December 06, 2006, 06:27:26 PM
It's #3.
Title: Re: *RB recording in a quiet environment*
Post by: amoergosum on December 06, 2006, 07:07:38 PM
Ah…I just found the mp3 bitrate corner in the new built.

I  did a short sample recording and I think the hissing issue
is gone.
Nice!
Thanks for your help!
Title: Re: *RB recording in a quiet environment*
Post by: Llorean on December 06, 2006, 09:38:42 PM
Never EVER report problems on unofficial builds, or problems you haven't verified with a new build. As can be seen, these problems don't alway even exist any more, and it's much simpler for you to quickly verify that the problem is stil there before getting other people involved.

And for clarity's sake, official builds are the ones you get at the Daily Builds or CVS Builds link on the left. Even if it's a build linked by an official member of the project, if it's not coming from the official build pages it is an unofficial build that they happen to maintain.
Title: Re: *RB recording in a quiet environment*
Post by: LinusN on December 07, 2006, 02:12:01 AM
To be honest, a forum post doesn't count as an official bug report. Nevertheless, as Llorean pointed out, you will save us a lot of work by:

Title: Re: *RB recording in a quiet environment*
Post by: amoergosum on December 07, 2006, 03:02:34 AM
To be honest, a forum post doesn't count as an official bug report. Nevertheless, as Llorean pointed out, you will save us a lot of work by:

  • Always trying the latest official build before reporting
  • Telling us which build and version you are using




guys...thanks anyway for your help.
I will do better in the future... ;)
Title: Re: *RB recording in a quiet environment*
Post by: petur on December 07, 2006, 05:11:16 AM
and using maximum gain on irivers is like... yuck... the amp is very noisy.
Title: Re: *RB recording in a quiet environment*
Post by: amoergosum on December 07, 2006, 06:41:12 AM
apart from the above, I can only recommend a good mic and an external mic amplifier

Hi Petur,
could you recommend one which would work well with
my external Sony Mic?
/Ben
Title: Re: *RB recording in a quiet environment*
Post by: Llorean on December 07, 2006, 09:51:55 AM
Well, while the forum doesn't count as an official bug report, we have made it clear in the guidelines that unsupported builds aren't to be asked about outside their individual threads.
Title: Re: *RB recording in a quiet environment*
Post by: petur on December 07, 2006, 11:48:13 AM
apart from the above, I can only recommend a good mic and an external mic amplifier

Hi Petur,
could you recommend one which would work well with
my external Sony Mic?
/Ben

I can only recommend taking your recording questions to http://www.taperssection.com. Registration is required (but free) even to read the forum but the people over there have tons of experience and (mostly) friendly ;)
Title: Re: *RB recording in a quiet environment*
Post by: Meow on December 16, 2006, 08:27:56 PM
and using maximum gain on irivers is like... yuck... the amp is very noisy.
I usually record 10 seconds without audio present, or with the mic/line plug pulled out, so I can remove the noise from the WAV later on. Works like a charm. You can easily get rid of at least 50% of the noise without damaging the rest of the audio.

Noise removal can be done with CoolEditPro/Audition and many other audio editors.