Rockbox Technical Forums

Support and General Use => Recording => Topic started by: perik on September 28, 2006, 03:32:05 PM

Title: effects in rockbox
Post by: perik on September 28, 2006, 03:32:05 PM
Hi!

Been using the rockbox on my Iriver H120 for recording and just have to say that the firmware is great.

Anyway, there are some things Im missing. Dont know if this is possible to do but say what you think.

Compressor - would be useful in some situation while recording
limiter - would also be great for preventing the signal to clip while recording.
reverb, delay etc - would also be nice in some situations.
eq, highpass filter

Ive also got some questions:
1) What does the prerecord time do? havnt figured that out yet.
2) What does the automatic gain control do? Well I guess it does what it says to do, control the gain automaticly but how? Does it work as a limiter or something like that?
3) what does the AGC clip time settings do?

Ok,

thanks for replies

Perik
Title: Re: effects in rockbox
Post by: pabouk on September 28, 2006, 04:42:43 PM
The players supported by Rockbox do not have any special hardware for recording preprocessing. Only the gain can be set during recording and it does not allow you to implement real compressor, limiter or even good AGC. :( Compressor or limiter would be done purely in software in this case and it is much better to process the recorded file (on PC). It would save a lot of precious battery life and allow you to use filters of higher quality - i.e. not limited by many compromises. In adition you would still have the original unprocessed file.

Answers for the questions

1: It enables pre-recording into a buffer so the recorded file will contain recording of the selected amount of time before you actually started the recording.

2: I do not know the algorithm exactly but basically it lowers or raises the gain when the input volume is over or under certain limit for a certain period of time.
Title: Re: effects in rockbox
Post by: Febs on September 28, 2006, 09:14:21 PM
I agree.   Even if the hardware supported something like this, I would prefer not to process my recordings on the fly.  I'd rather process them in post so that I had the original to work from if I didn't like an effect I added.
Title: Re: effects in rockbox
Post by: petur on September 29, 2006, 02:53:30 AM
Compressor - would be useful in some situation while recording
reverb, delay etc - would also be nice in some situations.
eq, highpass filter

As mentioned above, this is too CPU intensive (eats battery) and you would get much better quality during postprocessing on PC. There's no actual gain in implementing this in RockBox (unlike encoding which saves diskspace)

limiter - would also be great for preventing the signal to clip while recording.

would be pretty useless because the only clipping that can happen is in hardware and the pre-amp od the ADC. Rockbox as a basic AGC that has a 'Safety' mode to reduce gain if the signal is too hot.

1) What does the prerecord time do? havnt figured that out yet.

When you're in the recording screen, incoming signal is buffered in a loop. When pressing 'Rec' you can have up to 30 seconds prior to your buttonpress saved with your recording. That way you'll necer miss the start of what you want to record ;)

2) What does the automatic gain control do? Well I guess it does what it says to do, control the gain automaticly but how? Does it work as a limiter or something like that?
3) what does the AGC clip time settings do?

AGC controls the gain and has a few modes that indicate the speed at which the gain is modified. Clip time indicates the duration of 'hot signal' before the AGC kicks in.


Happy recording!