Topic: PCM-M10 Story - Is ALC Really This Good?

[stevetoney]

I bought an M10 a month or so back.  I've never used it other than initially fooling around with it, but after leaving for a gig this weekend I thought I remembered having it all setup properly.  I didn't really feel comfortable pulling the rig out and checking all of the settings (since I was late and hadn't had a chance to check taper friendliness of the band), so once the music started I just started rolling and checked to make sure my levels were rolling along well enough.

Maybe 15 minutes into the show, I began noticing that my levels were pretty consistently peaking perfectly and I hadn't really adjusted any level controls, so I began thinking something was up.  Sure enough, upon closer inspection I saw the 'auto' indicator in the window.  Dammit!  I'd left the Auto Level Control switch on.  Oh well.  I figured since I was 15 minutes in, might as well just leave it that way, so I left it the rest of the show.

After getting home, I also discovered that I'd operated with the mic switch on the 'high' sensitivity setting (better to use 'low' for loud gigs).  This was a very loud gig and I was right up front, so at that point I was almost 100% sure that with these two mistakes that my recording was hosed. 

Lo and behold, putting it up on Audition, the recording sounds nice and there is absolutely no modulation artifacts that I expected to hear from the ALC.  In looking at the waveforms in Audition, there are no squished peaks either.  Very strange!

I'm thinking that I probably just got lucky with my settings for this particular night, but right now I'm not really sure.  I mean, on one hand, it's hard for me to believe that with the sound as loud as it was and with my mic switch set on high, that ALC wouldn't have kicked in...not to mention that it's too unbelievable to think that my levels would have been perfect all night without some form of manual control, so it's pretty obvious that 'auto' had to have been functional. 

That said, having had bad experiences with ALC in the past, it's hard for me to believe that ALC works so well on the M10 that you wouldn't hear any artifacts at all, nor see any of the typical waveform truncation. 

Does anyone have any thoughts or has anyone else had positives or negatives to share with ALC on the M10?

Thanks in advance.

[fmaderjr]

I think you got lucky and I'm sure you must have been using mics that aren't very sensitive like Church Audios. A quick test with my home stereo using sensitive mics show that the ALC does not automatically keep the meters under 0db. If the M10 mic input is set to high, it doesn't take much for the recorder to generate a message telling you to set the sensitivity to low. Then if the source is pretty loud you get a message saying to move the mics away from the source.

[guysonic]

Apparently the ALC operates as a voltage controlled 1st amp stage gain with very wide operating range.  Electronically able to take the gain low enough to replicate the LOW manual switch setting avoiding all chances of overload.   

Still, depending on the type of sound/music, certainly this gain has a delayed release where the gain will eventually rise if the sound level drops for a long enough time, and this would be audible.   

Fortunately, your venue was at faily constant loudness so the ALC set up and didn't audibly change, so maybe a good thing for certain types of consant sound level recordings, but not for everything.   

Below are my M10 tips and particular is the part about taping over those switches!
------------------
TIPS: (For highest quality recording purposes)
 
Use M10 ONLY set in 24 bit recording mode.  Sample rate is your choice, but suggest using 44.1K sample rate if wanting best CD compatible editing options.
 
Use M10 ONLY with MIC INPUT sensitivity switch set in "LOW" taping over this switch to not be moved.  "HIGH" setting is way too much 20 dB boosted first stage gain giving inferior audio quality.  Even with very low VU levels, LOW setting gives cleaner more defined 24bit depth audio best boosted in post edit, NOT by using deck in HIGH setting.
 
Allow for having best headroom dynamics with NOT pushing recording VU levels.   Wise to ONLY push REC levels of master recording to -12 dB PEAK VU (not average, but maximum peak reading) so recording has best chance of never clipping even if much louder unexpected sound is encountered.
 
Use M10 in full manual (not AUTO, Limiter) record level control mode setting, suggest also taping over this switch so it does not move. 
 
Wise tact is to always engage HOLD feature so touching buttons do not accidentally stop recording until you're ready to stop the session. 
 
Do all editing in 24 bit mode, adjusting loudness and other changes desired.  Then as last software edit step convert copy of file to 16 bit if later doing CD storing this copy of file for disc burning purposes.
 
See taperssection.com M10 comments/tech data GuySonic posted at: http://taperssection.com/index.php?topic=130924.0;all 
--------------------------


Below is tips for using Sony M10 recorder:
------------------
TIPS: (For highest quality recording purposes)
 
Use M10 ONLY set in 24 bit recording mode.  Sample rate is your choice, but suggest using 44.1K sample rate if wanting best CD compatible editing options.
 
Use M10 ONLY with MIC INPUT sensitivity switch set in "LOW" taping over this switch to not be moved.  "HIGH" setting is way too much 20 dB boosted first stage gain giving inferior audio quality.  Even with very low VU levels, LOW setting gives cleaner more defined 24bit depth audio best boosted in post edit, NOT by using deck in HIGH setting.
 
Allow for having best headroom dynamics with NOT pushing recording VU levels.   Wise to ONLY push REC levels of master recording to -12 dB PEAK VU (not average, but maximum peak reading) so recording has best chance of never clipping even if much louder unexpected sound is encountered.
 
Use M10 in full manual (not AUTO, Limiter) record level control mode setting, suggest also taping over this switch so it does not move. 
 
Wise tact is to always engage HOLD feature so touching buttons do not accidentally stop recording until you're ready to stop the session. 
 
Do all editing in 24 bit mode, adjusting loudness and other changes desired.  Then as last software edit step convert copy of file to 16 bit if later doing CD storing this copy of file for disc burning purposes.
 
See taperssection.com M10 comments/tech data GuySonic posted at: http://taperssection.com/index.php?topic=130924.0;all 
--------------------------
Moe tips at www.sonicstudios.com/tips.htm

[fmaderjr]

Apparently the ALC operates as a voltage controlled 1st amp stage gain with very wide operating range.  Electronically able to take the gain low enough to replicate the LOW manual switch setting avoiding all chances of overload.   

I love guy's input here, but in my informal test posted above I did not find this to be the case. Using high sensitivity mics, with the recorder mic sensitivity at  low and holding the mics by a speaker, I did not have to turn the stereo volume up all that much to have the meters go over 0 dB and to get a message telling me basically to move the mics farther from the source. With low sensitivity mics, though, the volume would had to be a lot louder for this to happen.

And if you have the sensitivity switch set to high, the meters go over 0 dB with a lot less volume out of the speaker and you get a message telling you to switch the mic sensitivity to low.

[sctp]

It seems to me like the fundamental tradeoff here is:

The noise injected by higher pre-amplification levels
   vs.
Fixed noise levels added by the unit + quality loss experienced when expanding a digital signal in post

For example, if fixed noise were negligible and sample size were 64 bits, the best S/N might come from manually recording everything at record level 1 and expanding in post.  If fixed noise were high and we had to sample at 8 bits, the best S/N might come from using ALC.

If so, then the key question is how high are fixed noise levels in the M10 and how bad are quality losses from expansion of a 24-bit signal.

[Ozpeter]

As memory serves me, the "Auto" setting of the M10 can be replicated by setting the input level to "3" and turning the limiter on.  In other words, it's not what I'd call ALC, more a fixed low input level with the limiter catching the peaks.

[sctp]

Don't think so.  I ran a test.  1000Hz tone ascending 6dB every second to overload then descending.  Recorded the tone on Manual 3 with Limiter on and recorded the same tone with ALC.  Accidentally, there was a loud pop in the very middle, but that only helped to exaggerate the difference in how the signal was captured.

The manual setting lets the pop blow, while ALC captures it.  The manual setting captures identical levels regardless of ascending or descending volumes (the "shoulders" are the same height).  The ALC captures different levels depending on whether the volumes are ascending or descending (the "shoulders" are different heights...and on the right you can even see them creeping back upward).

Manual 3 with Limiter on:


ALC:

[jlykos]

I have the D50, not the M10, but I believe that the two units are similar.  Sony uses two A/D converters in the D50: one running normally and another running 12db down from the first.  When the first one goes over, the unit automatically switches to the second one as the limiter.  It is not really a "limiter" in the true sense, but rather provides an insurance policy if you briefly go over.  If you are consistently running reds and are like 20db over 0 for the entire recording, the limiter won't really have much of an effect.

[kleiner Rainer]

Hi all,

concerning the ALC issue, it helps to check out the codec datasheet of the PCM-M10:

http://www.cirrus.com/en/pubs/proDatasheet/CS42L52_F1.pdf

The "care and feeding" of the built in ALC is explained on pages 27 and 28.

BTW comparable codecs by Texas Instruments (as used in the Zoom H2 for example) also have ALC built into them.

Greetings,

Rainer

[Ozpeter]

Heh, I stand corrected, and very nice research, guys!

I note from the Cirrus Logic document that alc is applied (mostly) to the channels independently.  This would appear to give rise to the possibility of skewing of the stereo image if there was a significant difference in the sound level applied to one or other channel compared to the other.  I can't help wondering whether this is to do with the choice of omni rather than cardioid mics, as the former would be less prone to showing such imaging problems with ALC turned on (as it's harder to apply a significant level difference to those mics when mounted close).