M4 I/O and cables

[gbd]

Hi everyone, first post here.

I'm an amateur musician doing some simple home recording with my MOTU M4 via usb into an
old Macbook Pro running Performer Lite. I'm looking for recommendations on audio connections.

I'm primarily a guitarist and record guitar through a Line6 HX Stomp, configured for line level output,
via balanced TRS to line inputs 3 and 4 on back of the M4. That unit has good options for
setting output impedance and level and I've been able to use the nice metering on the M4 to find a good
recording level.

I've also picked up a synth keyboard as a 2nd instrument and would like to record that as well.
I'm pretty sure the synth (Roland
XP-30) has L/R unbalanced line outs. I'm currently connecting via unbalanced TS into the
mic/line/guitar inputs 1 and 2 on the front of the M4. This seems to be working fine, and I've got
the gain knobs at about 9:00 there with the synth volume slider at max. I'm wondering, though,
if I ought to be using a direct box, such
as the Radial ProD2 passive 2-channel DI, running TS from the synth to the DI, then XLR balanced into
the combo inputs on the front of the M4. I've also noticed that the headphone out on the synth
is absurdly loud, such that I have to just nudge the volume slider to barely above zero
(There might be a setting for this somewhere in the synth system menu). Maybe
I could be using a TRS/TS splitter cable from the headphone out?

I'm not interested in coloring the sound or questing for
tone improvements, and again, I'm able to record everything just fine.
I just want to make sure I'm doing everything properly in terms of signal level,
impedance, grounding, shielding, etc. I found this article from Soundonsound,
(https://www.soundonsound.com/sound-advi ... -keyboards), which generally does
recommend DIs. It seems one big advantage would be protecting my gear against accidentally hitting
the 48V phantom power buttons. But that article is a bit old and doesn't mention mic/line/guitar
combo inputs, as far as I can tell.

Please let me know if I'm fine as is, or if investing in a DI
and XLR cables would be wise. And, for that matter, am I connecting the HX Stomp correctly?
Maybe I should be going the other way around, sending an unbalanced instrument level out from that into
inputs 1 and 2 (using the 'guitar' capability), and sending TS from the synth into line
inputs 3 and 4? Maybe I'd be better off avoiding the M4 mic/line/guitar inputs altogether and
using the USB out of each unit into a USB hub on
the Macbook? Official literature recommends against using usb hubs. The 2nd USB port on the laptop is
already taken with a hub connecting hard drives, mouse, etc. I'm also open to the idea of finding
an interface with more inputs, but then again would want to know what kind of inputs I would
actually need.

Thanks for your help.

[mikehalloran]

First off: Do pay attention to the warning not to use balanced (TRS) cables with an unbalanced source. According to MOTU, Focusrite and others, you can fry your unit that way. Focusrite explains why in detail; MOTU just says Don't—some others don't even give a warning.

Unbalanced TS cables are fine. Neither balanced nor unbalanced cables will give you what you want, however.

The issue is not balanced vs unbalanced but the +18dBu fixed line level of inputs 3 & 4. There are a couple dozen manufactures who've released new "Fast USB 2" or USB 3 interfaces using this same DAC since October 2019 and every one of them has the same issue on their line ins. They are designed for true line level signals. Despite the claim that they can handle keyboards, they can't. I bought one of the first M4s and have been there with MOTU Support on this issue.

The Combi-jacks for 1&2 will handle it, same as a guitar DI. This leaves you two options:

a) get a DI with line level out as you expect. Use an XLR to TRS cable if you like but many DIs also have an unbalanced out — a TS to TS cable will be fine if it's quiet enough.

b) Use the Combi-jacks with a TS–TS cable on the front panel of the M4 for your synths and get a Mic Pre with a line level out for 3 or 4 (or a pair for 3 & 4).

I've tried both ways to crack this nut with the same degree of success.

[gbd]

Thanks @mikehalloran, that's very helpful. I'll be sure not to use balanced cables with an unbalanced source. And I'll be sure to read spec sheets on dbu ratings for line inputs. It seems not all 'line level' ins/outs are created equal.

[mikehalloran]

It seems not all 'line level' ins/outs are created equal.

True but with these new units, they are though some list the spec as +16dBu. At least one (Native Instruments) doesn't list it at all though it clearly is one of these as well.

Here are the clues: a) It came on the market September 2019 or later, b) no gain or input trim for the Line ins, c) nearly all have a blend/balance control for monitoring input and output d) advertising Fast USB 2 (except for the USB 3 Thunderbolt versions) for Near zero or Zero latency

These are great units and perform as advertised. If you do the math, you'll see that the claimed round trip differences between the slowest (Core drivers on the Mac) and the fastest (USB 3 and TB) is less than you'll get by moving your ears +/- 18" from your monitors. Of course, the marketing departments tell you that this is huge — yea, of course it is.

The only weakness, of course, is the fixed level on the Line Ins as you, I and others have found out. Even the Mackie version, ProFXv3 with 6–30 channels in has no gain for the Line Ins. Only the mic pres and Combi-jacks (and only two of those, even on the 30 channel version with 25 mic pres). C'mon, Mackie, would it have hurt to give us 4 Combi-jacks on, say the 12 channel? Also, unlike the M4, the ProFXv3 has only 2 channels out vs 4 on the M4.

[gbd]

I've just checked and the outputs on the Line6 are labeled 'balanced/unbalanced', so I think I'm ok on that front.

Let me see if I understand you correctly re: the dBu. On some newer products , the fixed-level line inputs are actually not specified correctly, or not performing as specified. So when comparing products, the combo mic/line inputs with a dedicated gain control will be preferable.

With the Line6 going into inputs 3/4, I do genrallly have to configure the main l/r output levels to at least +10db, sometimes more depending on the patch and which guitar or bass I'm putting thru it. I figured that was just the nature of the amp-modeling/multi-fx but it may actually be due to way the new line inputs are.

I haven't had any issues with latency.

[mikehalloran]

I've just checked and the outputs on the Line6 are labeled 'balanced/unbalanced', so I think I'm ok on that front.

Let me see if I understand you correctly re: the dBu. On some newer products , the fixed-level line inputs are actually not specified correctly, or not performing as specified. So when comparing products, the combo mic/line inputs with a dedicated gain control will be preferable.

With the Line6 going into inputs 3/4, I do genrallly have to configure the main l/r output levels to at least +10db, sometimes more depending on the patch and which guitar or bass I'm putting thru it. I figured that was just the nature of the amp-modeling/multi-fx but it may actually be due to way the new line inputs are.
.

More accurately, the level specs appear to be accurate but the marketing departments' claims that keyboards can be plugged in are wishful thinking.

You really need something that takes -10 outs and step them up to +4 levels. Sure, tons of DIs at many price points with all sorts of features that do this but what if all you really need is a box with a pair of great transformers?

The Ebtech LLS 2 from Morley is the 2-channel box I've been looking for. It does exactly what I need and no more. Specs are excellent and it's a lot less expensive than most other passive DIs. It comes in TRS only ($83), TRS+XLR in parallel—in case you don't have an adapter cable, I suppose ($105) and an 8 channel version ($349) for rack mounting. It's also known as the Morley MLS 2.

https://morleyproducts.com/wp-content/u ... 070717.pdf

I've bought 3 of them. My Yamaha P-121 has benefited the most (level way too low for my M4) but it makes my iPad sound great, too. The third one is used for a keyboard or Roland drum kit into 3&4 of an M4 (stereo — both can be run simultaneously if summed to Mono). They sound just as good into the line ins of my Mackie FxProv3 mixers.

• Frequency response 10Hz to 40kHz plus or minus 1dB into
10kOhm load
• Distortion less than 0.002% THD @ 1kHz
• Crosstalk better than –97dB
• Maximum source impedance 1kOhm. Minimum load impedance
10kOhm
• Cold Rolled Steel Housing
• One Year warranty

Radial preaches that one should use passive DIs for active inputs. I've always used passive DIs on keys and electronic drums.

Anyway, I like these a lot. There are some used here and there. Only one of mine was bought new.

[HCMarkus]

I didn't peruse the preceding back and forth in detail, but a quick review has me thinking y'all may be overthinking this a bit. Modern instrument manufacturers generally want to make interfacing their gear as painless as possible.

The HX Stomp has a "line level" output setting which sounds like it provides adequate gain into the M4 line inputs. Looks like plenty of gain for the keyboard in the front panel inputs, too. Both should work fine. The M4 has very high input impedance, similar to most DIs. Will a DI sound different? Try it and see. My guess is, if gain is matched, DI and direct sound will be indistinguishable. You might be returning that DI...

PS: Many keyboards and the Line 6 Helix can drive +4 inputs. My Yamaha S90ES and MotifES6 push plenty of level to drive line-level inputs. Output level can be adjusted within the keyboards' OS.

[mikehalloran]

Modern instrument manufacturers generally want to make interfacing their gear as painless as possible.

But they don't.

Perhaps I posted this in the wrong thread.

Many keyboards and the Line 6 Helix can drive +4 inputs. My Yamaha S90ES and MotifES6 push plenty of level to drive line-level inputs. Output level can be adjusted within the keyboards' OS.

My new Yamaha P-121, introduced fall 2018 cannot. I've confirmed this with Yamaha; MOTU support couldn't help me except to confirm that inputs 3&4 accept line level only and that there's no input trim of any kind. Its inability to generate a usable signal with the P-121 is what started me on this quest.