Rockbox Technical Forums

Support and General Use => Recording => Topic started by: clammer on March 24, 2009, 03:05:38 AM

Title: mic level input for iriver iHP140
Post by: clammer on March 24, 2009, 03:05:38 AM
Hello,

I just installed Rockbox on my iriver iHP 140, and was confused to discover that "source" in recording settings was limited to the following settings: FM radio, digital, line in, and internal microphone. Where is "external microphone"? Or am I missing something?

In the iriver firmware, there's an option for an external microphone, and when I plugged a shure SM57 (dynamic mic) into the line in socket, I could get a decent level. But I'm having to boost the gain to somewhere in above 30 dB to get an equivalent level on the line in setting in rockbox. Won't this introduce an unacceptable amount of noise?

I was hoping to use rockbox for my recordings, so that I can monitor and adjust levels more easily. It seems like tons of people use it for this, so I know I must be missing something basic/obvious. Or do all of you use mic preamps? I'd be open to getting one, but I was just confused as to why it seemed I could get a better level with the iriver firmware than with rockbox (which seems better in every other way).

thanks for your help!
Title: Re: mic level input for iriver iHP140
Post by: Multiplex on March 24, 2009, 04:39:02 AM
I'm no expert on recording - just an interested lurker, but I do remember lots of conversation on this topic, maybe here or maybe in the Wiki.

As far as I remember the iRivers H100/H300 have specific settings in the OF as you describe but they use the same input (the mic power is not even switchable, it's always on) and just apply lots of gain.

The developers decided that the OF pretence should not be followed and give you the inputs that the device has and allow you to adjust the gain as required.

If you do some searching there are some interesting discussions on how the gain is implemented.
Title: Re: mic level input for iriver iHP140
Post by: petur on March 24, 2009, 05:13:33 AM
Where is "external microphone"? Or am I missing something?

In the iriver firmware, there's an option for an external microphone, and when I plugged a shure SM57 (dynamic mic) into the line in socket, I could get a decent level. But I'm having to boost the gain to somewhere in above 30 dB to get an equivalent level on the line in setting in rockbox. Won't this introduce an unacceptable amount of noise?

I was hoping to use rockbox for my recordings, so that I can monitor and adjust levels more easily. It seems like tons of people use it for this, so I know I must be missing something basic/obvious. Or do all of you use mic preamps? I'd be open to getting one, but I was just confused as to why it seemed I could get a better level with the iriver firmware than with rockbox (which seems better in every other way).

Previous poster is correct; the original firmware has two source settings called line-in and ext. microphone, but the only difference is the gain range changes. So if you get good levels with the OF setting as ext microphone, you have to know that you are in fact using high gain settings without iriver telling you.

RockBox gives you the gain setting as the hardware offers. Up to +20dB the noise is acceptable. If you need more, or want to record very loud music, I advice to get an external mic amp.

(for the loud music: you need it because the 3.7V plug power might not be enough for the mic to function with high SPL levels and will brickwall)
Title: Re: mic level input for iriver iHP140
Post by: Meow on March 25, 2009, 05:09:39 PM
So, how hard can it be to integrate this REP into the 3.2 package?
Geez. I might try it myself, but it seems strange none of the devs are able to.
Title: Re: mic level input for iriver iHP140
Post by: petur on March 26, 2009, 04:23:31 AM
because the recording code changed significantly since the REP was created, and nobody maintains it. So the two got separated quite a bit.

The issue isn't difficulty, the issue is time. I've been merging it for some time but I'm not there yet. Life is very busy and the little kid at home consumes more time than I thought... ;)

Furthermore, the original REP was written for iriver, using almost fixed screen layouts. If we merge it in SVN, we must take into account all possible targets. A lot more work than a hack to get it on two players.
Title: Re: mic level input for iriver iHP140
Post by: Meow on March 26, 2009, 04:48:35 AM
I understand. If I can help with some trivial code copy-pasting tasks, let me know. I'm quite a code-cruncher and scripter myself, and a fast learner. One half of JTHZ: http://jthz.com/puter/software/

I own an iHP140 (iriver).