Recording Level vs Playback Level

[johnp_g]

Hello,

I've been a happy Rockbox user for a few years now and I'm really pleased at
the functionality improvements over the OF of the iRiver H120.

I record a lot of stuff via the line in socket, from shortwave radio
receivers etc. and adjust the recording gain to peak at Full Scale Deflection on the peak
level meter on the WRS. Audible distortion occurs if I increase the gain, or input level,
beyond this, so this would imply that the metering is a true indication of the input level, and it's limitations.

However, when playing back any of my recordings on the player, or on the PC in an editor such as Audacity, I see the amplitude is only 50% of the maximum.

I can use Audacity to normalize, i.e. amplify to put the peaks at "1" (100%), or more usually at -3dB of max, but I'd rather fix the peak levels at the recording stage, not afterwards.

I'm confused about the disparity between the recording level metering, and the playback level meters. Files that are amplified in Audacity to peak at "1" sound okay when played back on the iRiver, and the WPS peak level meters now reach the max deflection.

Am I doing something wrong? I generally turn AGC off, and adjust the input
level and/or gain to peak at 100% (on the WRS meters) for the loudest input signal I'm likely to have.

I've searched back through the forum "recording" section, and tried to trawl the mailing list archives for some pointers on this, to no avail.



Cheers,

John
Shetland UK

[petur]

Thanks for bringing this to the forum

I tried yesterday using mic-recording on my h380 and the signal was as saturated as the peakmeter indicated.

Can you verify that your peakmeter settings haven't been changed? You can set min and max peakmeter levels - this can cause the peakmeter to show 100% at 50% signal.

[johnp_g]

Thanks for the reply Petur!

I've just done some tests with a variety of sources (internal mic, external mic, FM tuner and line in fed from a Lindos Audio test set).

The confusion over levels appears to have been a misunderstanding of mine about the recording setting for "Channels: mono/stereo".

I select "mono" - since I only generally record mono sources, fed into one channel, and set the recording gain to give 100% on the peak meter on the channel concerned, playing back the file I notice it only registers 50% on the meter, on both channels! My confusion I think, about how stereo/mono recording and playback is defined?

If I record in "stereo" but only to one channel (eg Left) and again set the single channel to peak at 100% when recording the resulting file shows 100% level on that channel, and nothing in the other one.

How can I record a mono source, to a mono WAV file, and still have 100% amplitude on the output file?

I will start to record "single channel ,stereo" from now on.

Cheers,

John

[petur]

Ah, these details are interesting... I'll try to reproduce it this way as soon as I find the time

[petur]

I just reproduced this and I think the code tries to add the left and right channels together, so if you ave a 100% left and 0% right, you'll end up with a 50% waveform...

Maybe we should offer settings to do L/R/L+R if mono is selected?

[johnp_g]

Thanks Petur!

Yes, I came to the same conclusion, that the Mono recording was generated as L+R/2.

I made a new lead, stereo, to connect between my (mono) source that put the same signal on the L+R channels. Now when recording in MONO I get full amplitude playback in MONO. (100% on both channels in playback.)

I thought the MONO would just record one channel (the L) but seemingly this isn't the case, it's a mix of L and R together!

Yes, I agree that for my purposes (and others I assume) a menu setting of MONO: L, R or L+R/2 would be a good idea. How is it best to proceed with this request?

Thanks for the confirmation of my findings.

John

[petur]

Yes, I agree that for my purposes (and others I assume) a menu setting of MONO: L, R or L+R/2 would be a good idea. How is it best to proceed with this request?

I'm already looking into it

[johnp_g]

Yes, I agree that for my purposes (and others I assume) a menu setting of MONO: L, R or L+R/2 would be a good idea. How is it best to proceed with this request?

I'm already looking into it

Great News Petur!

Thanks for the help with this.

Cheers,
John

[petur]

Implemented!

Install the latest 'current build' and check out the 'Mono mode' setting in recording settings

[johnp_g]

Implemented!

Install the latest 'current build' and check out the 'Mono mode' setting in recording settings

Hi Petur,

I've compiled r18746 and installed it.

I see the recording options for the Mono Mode - great!

Recording a 100% Left channel signal, with the recording settings set for "Mono" and "Left", gives a 100% amplitude, mono, wav file when viewed in "Audacity".

This is great! 

Oddly, the WPS peak meter shows approx. 66% reading, on both channels, when playing the file back in the iRiver H120 itself?

The mono wav file looks good in Audacity though, so perhaps this is something to do with how the iRiver handles mono files?

I'm really pleased that you've taken the time to add this facility - thanks!

If you have any clues about why the player itself doesn't show the amplitude of the 100% mono recording when playing it I'd be glad, but anyway, you've really helped me!

Thanks again

John

[petur]

It could be that the peakmeter sampling has some averaging by the way it is implemented. I certainly made sure this isn't the case for the recording peakmeter - it always shows true max peaks - but I don't care really about the playback peakmeter accuracy