Another S/PDIF question

[peterschut63]

Hi Forum, Hi Line6.

 

I am close to buying a helix Rack with Helix foot controller.

It will be used in my small home studio/office space.

 

What I want to do is make the Helix my main USB sound card (now it is a Native Instruments Komplete 6, and sometimes my Yamaha THR10)

 

If I use the Komplete 6, I use the S/PDIF output to a TC BMC2 desktop DAC into a pair of KRK VXT6 speakers and the BMC2 also drives the headphone directly. This BMC2 sounds very decent and the level monitoring sits in the digital domain where 0dBFS is the maximum value.

 

A few questions:

I would expect that the S/PDIF output of the Helix routed as main output (kind of parallel to the XLR out) would be a mix of what is presented to the Helix via the USB and local inputs. In may case often a backing track mixed with the guitar.

An individual volume control for the USB source would be required then. Is this possible?

 

I would also expect that the SPDIF output would be routed before the main volume control directly out of the mix engine of the DSP's and would have no digital attenuation to preserve absolute audio quality. Is this correct or possible?

(this would be ideal when routing to the BMC2)

 

There is a block schematic of the I/O capabilities when used as an USB device. What I couldn't find is a block schematic of the routing capabilities of the Helix and see its inputs, loops and outputs with their routing options seen from the internal paths.  Is that available?

 

There were some treads about S/PDIF low volume issues (not sure if these were issues or wrong usage) but to me the internal DSP path is digital. maximum level is 0dBFS. If you use the Helix you need to make sure that the input A/D converter is used all the way up to maximum (or lets say -12dBFS) level when you hit the guitar to the max.

Then the DSP and all its engines do their thing mixing other sounds and that way never reach 0dBFS.

This is then the stream that should get out of the s/pdif output and only gets attenuated on its analog outputs that ideally has a few analog levels like +4dBu, +15dBu and +24dBu when you crank the volume up all the way to the max.

 

I couldn't find any data on maximum input or output levels.

 

Cheers,

Peter

 

 

 

 

 

 

 

[datacommando]

Hi Forum, Hi Line6.

 

I am close to buying a helix Rack with Helix foot controller.

It will be used in my small home studio/office space.

 

What I want to do is make the Helix my main USB sound card (now it is a Native Instruments Komplete 6, and sometimes my Yamaha THR10)

 

If I use the Komplete 6, I use the S/PDIF output to a TC BMC2 desktop DAC into a pair of KRK VXT6 speakers and the BMC2 also drives the headphone directly. This BMC2 sounds very decent and the level monitoring sits in the digital domain where 0dBFS is the maximum value.

 

A few questions:

I would expect that the S/PDIF output of the Helix routed as main output (kind of parallel to the XLR out) would be a mix of what is presented to the Helix via the USB and local inputs. In may case often a backing track mixed with the guitar.

An individual volume control for the USB source would be required then. Is this possible?

 

I would also expect that the SPDIF output would be routed before the main volume control directly out of the mix engine of the DSP's and would have no digital attenuation to preserve absolute audio quality. Is this correct or possible?

(this would be ideal when routing to the BMC2)

 

There is a block schematic of the I/O capabilities when used as an USB device. What I couldn't find is a block schematic of the routing capabilities of the Helix and see its inputs, loops and outputs with their routing options seen from the internal paths.  Is that available?

 

There were some treads about S/PDIF low volume issues (not sure if these were issues or wrong usage) but to me the internal DSP path is digital. maximum level is 0dBFS. If you use the Helix you need to make sure that the input A/D converter is used all the way up to maximum (or lets say -12dBFS) level when you hit the guitar to the max.

Then the DSP and all its engines do their thing mixing other sounds and that way never reach 0dBFS.

This is then the stream that should get out of the s/pdif output and only gets attenuated on its analog outputs that ideally has a few analog levels like +4dBu, +15dBu and +24dBu when you crank the volume up all the way to the max.

 

I couldn't find any data on maximum input or output levels.

 

Cheers,

Peter

 Hi Peter,

 

I really only just skimmed over your question - maybe I should have gone deeper, but it's a little late at night here.

 

At first glance this look to be overly complicated when the Helix should make it all really simple.

 

I cannot understand the need for 3 different options for DAC. That's signal chopping gone to the extreme - keep it clean!

 

The Helix makes 8 channels of digital audio available in/out on your computer or within the DAW of your choice, then simply connect your KRK monitors to the XLR or jack outputs on the rear of the Helix, jam your headphones in the Helix dedicated jack socket and your good to go. Play along to YouTube clips, iTunes, whatever, it just works. Everything else seems superfluous to me. That is unless I am completely misunderstanding this post. I've had my Helix (floor unit) rigged up like this since last November and it all works fine with the audio side of things. As for MIDI - well, don't get me started on that.

 

Download the user manual and check some of the options - it's free.

 

http://line6.com/support/manuals/helix-rack

 

Hope this makes sense and/or helps.

 

Good luck.

[peterschut63]

Hi DataCommando,

Thanks for your reply and indeed that would work.

(what a great forum is this by the way, very little shouting going on as I browsed the different treads)

 

There are a few reasons why I would like this?

The MBC2 gives a very good idea of where you are in the digital domain with its nice meters

The built in DAC sounds great

I use it to listen to another device when the computer is not on (via its Toslink input)

 

The different output options for the DAC have all to do with making the best use of the digital domain resolution.

Unless the Helix has a true analog output gain section (which I don't think it has) it can be quite brutal if the outputs are referenced for instance to +24dBu @ 0dBFS that the digital attenuation has to back down 28dB because the connected speakers only need -4dBu (consumer level) to go full power.

My KRK's can be adjusted in the analog domain but not all speakers can.

A good practice would be to crank the volume all the way up on the Helix and attenuate on your speaker for best dynamic range and minimal noise.

This is what I did with BMC2.

 

The audio community made quite a mess of analog audio levels and when digital sound entered the market with zero headroom above 0dBFS the mess only got worse.

I know this as I designed A/D and D/A converters for the broadcast television industry and these guys are very picky about their reference levels. 

 

The helix will have 24 bit performance but no A/D or D/A converter that we can afford has 24 bit performance.

Most are in the region of 19 to 20 bit with 110dB dynamic range.

The used codec in the helix has a typical dynamic range of 111dB. If you feed the chip 20db below it rated input you are left with only 91dB, With guitar signals this will be very normal. if you then use the output D/A conversion as well 20dB below rated because your speakers are sensitive you lower the dynamic range even more.

I would say 90dB is great for overall system performance and will sound quieter than any tube amp, but 70dB isn't great.

 

I hope this makes sense.

[datacommando]

I know this as I designed A/D and D/A converters for the broadcast television industry and these guys are very picky about their reference levels. 

 

I hope this makes sense.

 

Hi again Peter,

 

Well, ouch! You just hurt my head with all that physics stuff - I just mess around with my Helix until I think it sounds good. There are no index marks on the main volume control, so it may well go all the way up to eleven - I dunno, mine never gets past about one third of the sweep. Come to think of it, I don't even recall seeing a full tech spec, schematic drawing for the Helix so all that "attenuation" stuff is above my pay grade.

 

There are a whole bunch of people on here that will have a much better idea, and be able to give you proper answer to your query.

Here's a good example from another thread -  It was posted by Digital Igloo (a Line 6 Product Manager), he would most likely know. Thing is, he got married recently and is otherwise engaged at the moment!

 

This is from Helix's electrical engineer:

 

The XLR outputs, when set to line level, are 20Vpp max, which is approximately +19.2dBu. So if you want to talk about nominal levels, you can say that’s +4dBu nominal with approximately 15dB of headroom. The ¼†outputs are exactly the same levels when set to line level, except unbalanced.

 

XLR outputs are balanced. Another thing to consider is Helix's Guitar Input, which has > 123dB of dynamic range (due to patented circuitry), which is industry-leading.

 

And here's another example response about "nominal output level".

 

That's correct. If you switch your speaker to +4, that means it's expecting a hotter signal, so it'll turn down its input sensitivity and be quieter.

 

-10dBV and +4dBu are just analog voltage level standards. Any given analog audio signal (such as the analog output of your Helix plugged into the analog input of your speaker) may be at, between, or outside these levels in amplitude at any given moment, as determined by the nature of the sound itself, plus any volume controls it passes through.

 

As long as the signal does not overload the speaker's input and cause unwanted clipping distortion, you should be OK using either the -10 or +4 setting.

 

More info (maybe more than the average person would care about) here: https://en.wikipedia...wiki/Line_level

 

Let's hope one of these real techie guys on here can point you in the right direction - sorry I can't help more, than this.

 

Right - I'm off now, and I'm just gonna make mine louder!

 

Good luck.

[peterschut63]

Thanks again Datacommando.

This is indeed part of the information I was looking for. The spec of the guitar input is at least very very impressive.

 

Coming back to my original question to this forum and Line6?

 

Is the s/pdif output attenuated as the main output? kind of runs in parallel?

In my preferred setup I will have then two volume controls in series. On the other hand I can crank the digital out to be full and control always the main volume with my TC BMC2.

 

@line6 Digital Igloo; happy honeymoon, and when you are back to it would a block schematic of the Helix be something you can share?

It would help a lot with understanding the routing and in/output options.

 

Cheers, Peter

[bjnette]

On the POD HD 500s the s/pdif can be attenuated from it's default zero under a global output menu.

The normal unattenuated output is equivalent to the master volume being fully open. Not sure on the Helix.

 

s/pdif would be a feed off from the Analogue to Digital Converter chip only. It being digital can go into your interface with a coaxial s/pdif input; or a toslink to coaxial converter will be needed to connect if toslink.

 

You can control this as you have stated.

 

It looks like the Helix also can act like a multi interface into your computer and DAW and back if desired.

[datacommando]

Is the s/pdif output attenuated as the main output?

 

Hi Peter,

 

Well, this S/PDIF thing intrigued me a little, so I went down to the studio and sparked up the Helix and had a poke around in the Global Settings options.

 

Under the Ins/Outs section on the 3rd page, Knobs 5 and 6 are allocated to "Digital Output" and "Digital Out Level" respectively. Knob Five switches between the choice of using S/PDIF or AES/EBU and number 6 can dial in an output level between a low of -60.0dB and a high of +18dB. The default setting on these 2 items are S/DIF and 0.0dB. A little more investigation reveals that on the First Page, Knob 6 is assigned as a "USB In 1/2 Trim" option also with a 60.0dB to +18dB range.

 

I would imagine this is bound to make sense you and other techno minded boffins alike - Me, I'm going to hang up the white coat and I'm off to make a racket!

 

Hope this sheds a little light.

 

Good Hunting

[peterschut63]

Under the Ins/Outs section on the 3rd page, Knobs 5 and 6 are allocated to "Digital Output" and "Digital Out Level" respectively. Knob Five switches between the choice of using S/PDIF or AES/EBU and number 6 can dial in an output level between a low of -60.0dB and a high of +18dB. The default setting on these 2 items are S/DIF and 0.0dB. 

 

 

That is indeed the part I was looking for.

So the main volume control on the front of the Helix does not attenuate the s/pdif output when that is chosen as the main output?

[duncann]

That is indeed the part I was looking for.

So the main volume control on the front of the Helix does not attenuate the s/pdif output when that is chosen as the main output?

 

The main volume knob on Helix does control the spdif volume. Relative to other outputs such as the 1/4" or XLR it is quieter though, when the newly added global spdif level is at 0dB - I have to dime Helix's volume knob.

[peterschut63]

The main volume knob on Helix does control the spdif volume. Relative to other outputs such as the 1/4" or XLR it is quieter though, when the newly added global spdif level is at 0dB - I have to dime Helix's volume knob.

 

Okay, thanks dunncann

I understand that this is an option, but in my opinion it should also be possible to have it fixed with zero gain or attenuation.

Ideally separate from the XLR outputs. So the XLR source the live speakers and are gain controlled and the S/PDIF has a fixed output to a recorder for instance.

[datacommando]

The main volume knob on Helix does control the spdif volume. Relative to other outputs such as the 1/4" or XLR it is quieter though, when the newly added global spdif level is at 0dB - I have to dime Helix's volume knob.

 

Seems like "duncann" has gone down this path - and this is what he discovered. I can't comment further, I've never been there, too complex for me.

 

Okay, thanks dunncann

I understand that this is an option, but in my opinion it should also be possible to have it fixed with zero gain or attenuation.

Ideally separate from the XLR outputs. So the XLR source the live speakers and are gain controlled and the S/PDIF has a fixed output to a recorder for instance.

 

Although, Peter, what you state here makes sense to me. I would think from what I've seen - the large volume knob controls the audio signal flow to the XLR or jack outputs to your monitor speakers, just like the small one sends a variable output through to your headphones, so it makes sense that the output flow to S/PDIF can be managed/trimmed via the Global Digital Output Level. I guess, that should be how you can balance the signal paths. This seems to be what is inferred in the latest Owners Manual Revision D. Please note I removed my Lab Technicians white coat earlier, so I may be well off the mark here.

 

Later guys - I'm going for a beer!

Let me know how it goes!

[duncann]

Okay, thanks dunncann

I understand that this is an option, but in my opinion it should also be possible to have it fixed with zero gain or attenuation.

Ideally separate from the XLR outputs. So the XLR source the live speakers and are gain controlled and the S/PDIF has a fixed output to a recorder for instance.

 

There is another global option to set what the volume knob controls: multi, 1/4"+xlr, 1/4", xlr, or digital. That in combination with the digital output level (global option) would make one way of adjusting each output level independently. Another way would be to adjust the level on each output block in the preset, assuming there is a separate output block for each output type. If there isn't you can add another output block if there is room to do that by splitting the path at the end of the signal chain.

[bjnette]

Wow. that sure is a thorough option being able to assign s/pdif level matched to the mains if desired.

 

Being able to increase the digital output would be of use for very high end interfaces for high res recording unless zero matches a midpoint volume on the main out volume?

[peterschut63]

I am a bit puzzled now datacommando and duncann.

 

I checked the rev D manual and I saw the different output options, multi, XLR only or 1/4"only.

There was no reference (as far as I could see) what the volume control knob controls. Did I mis something?

So Multi would be the default setting of our setup, but the volume control should only control XLR and/or 1/4"

 

So if you increase or decrease the volume and it affects the s/pdif output does the display show how much?

 

 

On a side note (@bjnette); increasing the s/dpif output level is a nice option but should ideally be omitted.

There is nothing wrong with digital gain, but if you drive the Helix well you should not need to adjust the level in the digital domain.

There is no such thing as midpoint digital volume. Your guitar sound and added effects should fit as close as possible to the maximum level the digital domain can handle (= 0dBFs = Full scale) as that will give the best dynamic range and lowest noise.

The digital domain should never clip as that is a very nasty distortion.

I am not sure if I make any sense but what I am trying to say is that the Helix (and any other digital device) has an internal resolution. If it is 24 bits the dynamic range is 144 dB. The highest volume is 0dBFs the lowest volume is then -144dBFs

To make use of this resolution your analog input signal needs to be referred to this.

If the absolute maximum level out of your pickup is 1Volt then ideally this 1 Volt should represent a dBFS value as close as possible to 0dBFs.

In practice this will be a few dB lower like -6dBFs or -9dBFs to allow for some headroom.

 

Sorry to keep on mumbling about this but recording digitally direct out of the helix should be with a digital level as high as possible.

This means the loudest peak attack of your guitar should be as close as possible to 0dBFs. If the Helix represents one of the many tracks that are recorded the mixing should make the level lower as every added track will increase the total volume. But attenuation in the digital domain is always better than having to increase the volume. 

[datacommando]

I am a bit puzzled now datacommando and duncann.

 

I checked the rev D manual and I saw the different output options, multi, XLR only or 1/4"only.

There was no reference (as far as I could see) what the volume control knob controls. Did I mis something?

So Multi would be the default setting of our setup, but the volume control should only control XLR and/or 1/4"

 

So if you increase or decrease the volume and it affects the s/pdif output does the display show how much?

 

Well the only info I can find regarding this stuff is on page 22 of the manual and then page 50 which states:

 

6 Digital Output Level: Sets the S/PDIF and AES/EBU output level. Normally, this should be left at 0.0dB.

 

That is the only reference in the entire manual, or anywhere else I checked.

 

This looks like one for Digital Igloo (appears he co-authored the manual) - Eric, where are you? Your assistance is required.

 

I think I saw him leave a post on here yesterday so, I would suggest that you send him a Personal Message, although I think he will say that all this stuff classified, trade secret stuff that he cannot divulge, but you never know!

 

As for the visual display of signal levels - well that seems to have been requested several times and is up on the IdeaScale pages.

 

The alien intelligence that came up with this Helix machine must have slipped back into their own dimension and taken the wiring diagrams with them. ;)

 

Happy trails.

[duncann]

I am a bit puzzled now datacommando and duncann.

 

I checked the rev D manual and I saw the different output options, multi, XLR only or 1/4"only.

There was no reference (as far as I could see) what the volume control knob controls. Did I mis something?

So Multi would be the default setting of our setup, but the volume control should only control XLR and/or 1/4"

 

So if you increase or decrease the volume and it affects the s/pdif output does the display show how much?

 

For output options there is also digital (spdif, aes/ebu, or l6 link), send 1/2, send 3/4, usb 1/2, usb 3/4, usb 5/6.

 

There's a few options for what the volume knob can control depending on the "Volume Knob Controls" global option. Those options are: multi, 1/4"+xlr, 1/4", xlr, or digital.

 

There is no integrated meter display as datacommando mentions.

[peterschut63]

For output options there is also digital (spdif, aes/ebu, or l6 link), send 1/2, send 3/4, usb 1/2, usb 3/4, usb 5/6.

 

There's a few options for what the volume knob can control depending on the "Volume Knob Controls" global option. Those options are: multi, 1/4"+xlr, 1/4", xlr, or digital.

 

There is no integrated meter display as datacommando mentions.

 

Hi Duncann,

 

But that is great news, meaning that if you select XLR, only the main output of the Helix is influenced and the S/PDIF is left alone. Right?

This is not clear from the manual but I expect adjustable in the global settings menu somewhere.

This would answer my question and solve what I want to achieve.

 

Another good thing of using the S/PDIF output at a fixed 0dBFs level is that the TC BMC2 will show the digital domain volume.

So it monitors headroom and any clipping that might occur in the DSP engines.

 

Thanks.

 

So I can go to the beach now, as I am on holiday in Curacao (but brought my guitar and Yamaha THR10)

[duncann]

Hi Duncann,

 

But that is great news, meaning that if you select XLR, only the main output of the Helix is influenced and the S/PDIF is left alone. Right?

This is not clear from the manual but I expect adjustable in the global settings menu somewhere.

This would answer my question and solve what I want to achieve.

 

Another good thing of using the S/PDIF output at a fixed 0dBFs level is that the TC BMC2 will show the digital domain volume.

So it monitors headroom and any clipping that might occur in the DSP engines.

 

Thanks.

 

So I can go to the beach now, as I am on holiday in Curacao (but brought my guitar and Yamaha THR10)

 

When the XLR output is selected, it would become the output controlled by the large volume knob, or the main output if that is what you want to call it, so you're exactly correct.

 

In addition, if you need to adjust the spdif level (-60dB to +18dB), that can also be done via a global option.

[datacommando]

When the XLR output is selected, it would become the output controlled by the large volume knob, or the main output if that is what you want to call it, so you're exactly correct.

 

In addition, if you need to adjust the spdif level (-60dB to +18dB), that can also be done via a global option.

 

Good work "duncann" - you got it figured for him, so it seems to make sense.

 

Now he's going to put his toes in the sand. What a life?

 

Me, I'm going in for the "studio tan". :)

[peterschut63]

back from the beach ...... haha

 

Thanks Duncann and datacommando.

 

It seems that the unit has more adjustments than the manual shows. This is not uncommon in designs with a software core.

The guy for the manual has a hard time keeping up with the enhancements of the software/PM team.

 

Cheers.

[musicimpossible]

My Helix Rack is spdif into an old Eleven Rack and then into my iMac (Pro Tools). My stock recording levels seemed to rather low coming from the Helix (using any preset) so I had a few choices. I opted with cranking the Helix Digital Output from the stock 0.0db to 7.0 db. I am not a techie, just go with what sounds good to me. That level is working great for me. 

[FlyingsCool]

I just had the same issue during a live band recording senario (we like to record our jam sessions).  Tried recording the Helix using S/PDIF into an interface last night.  I didn't have time to really sit down and understand the whole routing scheme and associated options for controlling levels from the various outputs of the Helix.

 

My setup

L2t connected to Left XLR, amp connected to right 1/4 output, Les Paul connected to Guitar in, JTV-69 connected to VDI (one of them volume set to zero depending on which guitar is being used).  Helix connected to computer through USB (I may have disconnected this at some point, remembering there was some situation that turned off one of the outputs so you couldn't create an infinite feedback loop).  S/PDIF connected to Focusrite 6i6.  Focusrite 6i6 set as input for DAW (Mixcraft 7).

 

I couldn't figure out how to get reasonable gain from the S/PDIF channels,  Volume knob on the Helix was at about half.  After recording, I had to boost the S/PDIF track by about 12 to 18 dB to get reasonable gain from it. 

 

I'm assuming I needed to disconnect it from the Volume Knob to get close to true 0 dB levels from it into the interface?

Can I do that if I want the Volume knob to control multiple outputs?   (I'm trying to avoid using an XLR to 1/4 adapter cable, I hate extra connections)

 

Can I still use the S/PDIF output if I have the Helix connected to my computer by USB (so I can use the Editor)?

[duncann]

I'm assuming I needed to disconnect it from the Volume Knob to get close to true 0 dB levels from it into the interface?

Can I do that if I want the Volume knob to control multiple outputs?   (I'm trying to avoid using an XLR to 1/4 adapter cable, I hate extra connections)

 

Can I still use the S/PDIF output if I have the Helix connected to my computer by USB (so I can use the Editor)?

 

You shouldn't have to keep the big volume knob from controlling the SPDIF, although you can with the global option, 'volume knob controls'. I have the volume knob maxed when I use the SPDIF and I get decent enough levels. You can also increase the 'digital out level' with the global option.

 

Yes you can use the SPDIF at the same time as the USB.