Topic: Microtrack and line levels

[yousef]

I know I've already brought this up in another thread but the more I ponder it, the more it bugs me...

As far as I can tell, the 1/4" TRS "line-in" inputs on the MT can't take a consumer level line-in (-10dB?), let alone the +4dB level that many mixing desks will be putting out.

As I understand it from other postings here, this is because there is a constant +14dB of gain on the TRS inputs. So if you were recording from the desk you would have to first attenuate the signal in order to allow the MT to boost it? Doesn't sound like an ideal signal path to me.
 
And, given this, what's the point of the +27dB TRS boost option? Has anyone here ever had to use it?

I know that mic inputs that can't cope with a mic signal in the live setting are par for the course but a line-in that's been designed so that it can't take a line level just seems bizarre.

Is there any hope of a way this could be circumvented - either through firmware or a physical modification?

Yousef

[Chris K]

hi. i made my first soundboard recording with the microtracker @ 24/48 a few weeks back. you are right the microtracker does not accept line level signals (my main gripe about this device).

i did have a set of 20db attenuators on hand which was the key. basically ran 1/4" tape outs from board > 20db attenuator > 1/4" ins on microtracker. in the 1st set i had it set to the M on the L/M/H switch and this was a little hot as i had the level at the very lowerst/far-left setting. Wavelab shows the recording hit 0db a few times but it doesnt appear to affect the sound (no harsh diginoise that i could detect)

the 2nd set i ran on the L setting of the L/M/H switch and seem had better control of levels (was probably just right of center on levels meter) and only got to -1.5 or so in the recording.

in either case i did not have the +27db digital boost option engaged. actually i have never used the +27db boost option and surmise i only would use that option if recording nature or very low sound levels. even if that were the case i'm not sure i would use it. perhaps if it were -27db cut...then maybe i would use it.

the recording i am referencing can be found here:

http://www.archive.org/details/lotus2007-01-27

 

[yousef]

perhaps if it were -27db cut...then maybe i would use it.

 

Thanks for the reply. Just wanted to be sure that this was indeed a bizarre piece of design rather than some sort of foolishness on my part.

I'll be giving your recording a listen.

Cheers,

Yousef

[Church-Audio]

perhaps if it were -27db cut...then maybe i would use it.

 

Thanks for the reply. Just wanted to be sure that this was indeed a bizarre piece of design rather than some sort of foolishness on my part.

I'll be giving your recording a listen.

Cheers,

Yousef

Its because they had to make the "line inputs" mic inputs as well. Its hard to make a dual input that is both a line input and a mic input. Especially when your controlling the gain via software not hardware. That is the crux of any recorder design.. IMO if anyone is looking for a real recording device pick one that has a line input and not a combination of the two via one socket. Its pretty dam hard to balance the needs of a mic input -40 or more with the needs of a line input -10 or more.

Chris Church

[willndmb]

i recorded a show from sirius radio line out > MT 1/4 with no probs at all
was i lucky or do i not understand something

[yousef]

IMO if anyone is looking for a real recording device pick one that has a line input and not a combination of the two via one socket. Its pretty dam hard to balance the needs of a mic input -40 or more with the needs of a line input -10 or more.

I'm pretty sure that in the publicity leading up to the MT's release, it was claimed that the line-ins would be able to cope with +4dB... Of course this could've been misinterpretation by pundits rather than an actual claim by M-Audio.

Still, it's actually marked as "line in", isn't it? I could've accepted one that could take a consumer level signal but not 4dB but calling this a "line in" seems pretty inaccurate to me. I mean, why not have designed it so that the mic-in (all but useless in taping loud music) had the characteristics of the line-in and then have the TRS inputs as a true line-in?

Yousef

[guysonic]

MT handles at least +3.2 dB LINE level with proper switch settings for TRS input.  Look at the input chart on review at www.sonicstudios.com/mt2496rv.htm

[yousef]

MT handles at least +3.2 dB LINE level with proper switch settings for TRS input.  Look at the input chart on review at www.sonicstudios.com/mt2496rv.htm

But when I had mine set to 1/4" inputs, "L", +27dB boost off, phantom power off and levels set as far to the left as possible, I got distortion when recording from two different radio stations and two different cds. The only time I didn't get clipping was when playing a very quiet disc.

So what am I doing wrong? 

Yousef

[Brian Skalinder]

But when I had mine set to 1/4" inputs, "L", +27dB boost off, phantom power off and levels set as far to the left as possible, I got distortion when recording from two different radio stations and two different cds. The only time I didn't get clipping was when playing a very quiet disc.

So what am I doing wrong? 

Perhaps the playback device is outputting > +3.2 dB.  What playback gear is in the signal path between FM/CD and the MT?

[yousef]

Perhaps the playback device is outputting > +3.2 dB.  What playback gear is in the signal path between FM/CD and the MT?

Just a Sony amplifier (TA FE 370) - but I've never had any problems with the levels it puts out with my D8, Sony home DAT deck or Iriver h320. And I know for a fact that the D8 won't take an unattenuated +4dB.

Could this be anything to do with using standard mono jacks in the TRS sockets?

[Roving Sign]

Perhaps the playback device is outputting > +3.2 dB.  What playback gear is in the signal path between FM/CD and the MT?

Could this be anything to do with using standard mono jacks in the TRS sockets?

Well - you're not balanced then - not really using the TRS...just TS - so probably affects something...

[Church-Audio]

Perhaps the playback device is outputting > +3.2 dB.  What playback gear is in the signal path between FM/CD and the MT?

Could this be anything to do with using standard mono jacks in the TRS sockets?

Well - you're not balanced then - not really using the TRS...just TS - so probably affects something...

Depending on how the MT input circuit is designed you can lose as much as 6db going unbalanced. Here is the part that freaks me out.. How can you have a mic input with phantom ( input impedance should be about 150 to 600ohms) Balanced. And then have that same input (line in) be 10k like it should if its a true line input? I think this is the real issue its one of input impedance. I would like to know what input impedance Guy Sonic used to test the distortion levels of the MT with was it 10k or 600ohm because a mismatch in input impedance would give you very different results in your distortion measurements and a "assumed increase" in headroom.

[guysonic]

Perhaps the playback device is outputting > +3.2 dB.  What playback gear is in the signal path between FM/CD and the MT?

Could this be anything to do with using standard mono jacks in the TRS sockets?

Well - you're not balanced then - not really using the TRS...just TS - so probably affects something...

Depending on how the MT input circuit is designed you can lose as much as 6db going unbalanced. Here is the part that freaks me out.. How can you have a mic input with phantom ( input impedance should be about 150 to 600ohms) Balanced. And then have that same input (line in) be 10k like it should if its a true line input? I think this is the real issue its one of input impedance. I would like to know what input impedance Guy Sonic used to test the distortion levels of the MT with was it 10k or 600ohm because a mismatch in input impedance would give you very different results in your distortion measurements and a "assumed increase" in headroom.

All tests used 1000 ohms input termination.

Make sure you're using latest MT v1.4.5 firmware as original shipped version firmware had the "L/M/H" switch settings reversed explaining your problem with LINE level overloading.

[yousef]

Make sure you're using latest MT v1.4.5 firmware as original shipped version firmware had the "L/M/H" switch settings reversed explaining your problem with LINE level overloading.

Yep, I'm using 1.4.5, downloaded just over a week ago.

Chris, when you say that you can lose up to 6dB by going unbalanced, do you mean losing 6dB of headroom (which could explain my problem) or 6dB of signal?

[yousef]

Speaking of the balanced inputs, I notice that Soundpros' MT adaptors use standard mono jacks:

http://www.soundprofessionals.com/cgi-bin/gold/item/SP-MICROTRACK-MINI-TRS#
http://www.soundprofessionals.com/cgi-bin/gold/item/SP-MICROTRACK-INTERFACE

I'm presuming that there must be some issue with plugging an unbalanced cable into the TRS input but I'm not sure exactly how these things work - can anyone explain for me? As I understand it, the 'balancing' involves two out of phase signals, one of which is inverted at the destination. So if you plug a mono 1/4" jack into a balanced TRS socket, the same signal goes to both tip and ring components of the socket, one gets inverted and then they are added together = some sort of phase cancellation?

If this is the case, (i) shouldn't clipping when using the MT's 1/4" inputs be less likely when using an unbalanced lead and (ii) why are Soundpros using the mono jacks?

I'm really very confused now - someone please put me right...