You are here

Digital I/O for Edirol UA-101?

For anything relating to music-making on Windows computers, with lots of FAQs. Moderated by Martin Walker.

Re: Digital I/O for Edirol UA-101?

Postby BillB » Tue Jul 18, 2017 8:14 am

Thank you, Martin. Yes, that's very helpful Indeed. If it's good enough for you... :geek:

A bit of rummaging on the internet "audio interface optical I/o" eventually showed that the Emu 0404 USB (as reviewed by your own fair hand in 2007) would make a good standalone AD/DA interface, as it has optical built in, so one less converter box to worry about. Need to go off and scout for a cheap one. I'll probably hook up a little Sony digital recorder I have, for capturing noodlings. (Would have used an old minidisc deck, but they are a bit too big to fit into my box room studio.)

The 0404 could also be pushed into service as an extra pair of inputs, if I really want 10 simultaneous tracks - with Hugh's jittery warning above, noted!

Incidentally, I tracked down one of Hugh's articles from April 2003 on digital clocking, in case it is of interest or use to others passing this way:
https://web.archive.org/web/20150609004 ... ocking.asp
BillB
Frequent Poster
Posts: 521
Joined: Mon Apr 07, 2003 12:00 am
Location: East Yorkshire

Re: Digital I/O for Edirol UA-101?

Postby ef37a » Tue Jul 18, 2017 8:42 am

Hugh, ref "clock loop"? A couple of years ago I had two desktop PCs equipped each with a 2496 card. There was a S/PFIF coax cable (75R PTFE insulated cable, super stuff!) to and from each RCA connector.

We, son and I, could exchange digital signals across each computer each way, that is, one could be source and one destination as required.

I am pretty sure the 2496 card selected the S/PDIF input as and when 'told to' by the software?

Bill: I have quite a few MDiscs, PM if you want some.

Dave.
ef37a
Jedi Poster
Posts: 9574
Joined: Mon May 29, 2006 12:00 am
Location: northampton uk

Re: Digital I/O for Edirol UA-101?

Postby Hugh Robjohns » Tue Jul 18, 2017 10:12 am

BillB wrote:Changed the UA-101 from 44.1 to 48khz sample rate, still a good signal on the MD - presumably it has built in sample rate conversion?

Seems likely -- as far as I can remember, a lot of MD recorders did have SRCs.

One specific question, is there any particular advantage to using 44.1 or 48khz? I seem to recall, many years ago, that there were arguments about avoiding resampling from 48 to 44.1 when burning CDs. Has that argument been consigned to the great format archive in the sky?

Sample rate conversion is generally very good these days, and so converting between different sample rates isn't as big a deal anymore -- although it must be said that not all software SRCs are as good as they should be. The http://src.infinitewave.ca/ website makes interesting reading. You can compare different software converters -- I'd suggest using the iZotope RX plots as a reference as they offer pretty much a perfect example of how it should be done!

As to choice of sample rate, 48kHz is mandatory if you're working with video, and 44.1kHz for CD and most consumer downloads. Sound quality-wise, there really isn't anything to choose between them in practical terms, and modern converters running at 44.1 generally deliver excellent results.

There are a few specific situations where, for ultra critical applications, 96kHz capture can offer some small sonic benefits, but often the extra processing and storage overhead is a more important consideration. Non-linear signal processing (like dynamic control) also benefits from higher sample rate working, but most DAW plugins (and many hardware digital mixers) employ transparent internal oversampling/decimation for that anyway.

For most things, I record at 44.1k. Video-related tracks at 48k, and specialist stuff at 96k.

H
User avatar
Hugh Robjohns
Moderator
Posts: 21963
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound

Re: Digital I/O for Edirol UA-101?

Postby BillB » Wed Jul 19, 2017 12:35 am

Dave, thanks for the kind offer of Minidiscs (I assume you mean discs, not players!). I think I have enough thanks, but I'll check and let you know if not.

Hugh, thanks for the further clarification on sample rates. The 44.1 general, 48 video and 96 special, is especially helpful, I might even manage to remember that.
:headbang:
BillB
Frequent Poster
Posts: 521
Joined: Mon Apr 07, 2003 12:00 am
Location: East Yorkshire

Re: Digital I/O for Edirol UA-101?

Postby Hugh Robjohns » Wed Jul 19, 2017 11:21 am

All converters these days are delta-sigma types, which sample at stupidly high rates (with a low wordlength) and then internally decimate the signal to the required sample rate and wordlength. This arrangement is massively more accurate and consistent than the crude (by today's standards) multi-bit converters of a couple of decades ago.

However, the vast majority of delta-sigma converter chips are 'half-band' types -- for computational simplicity in the digital filtering -- which means that instead of providing >100dB attenuation at the Nyquist frequency, they only manage 6dB of attenuation.

Clearly, this fails the Nyquist requirements (let nothing through above half the sampling rate), but in practice it's a bodge that can usually be tolerated because there is rarely any significant sound going into the converters above 20kHz. Most microphones have a plummeting sensitivity at that frequency, and most musical sources exhibit a falling energy spectrum anyway.

So, in practice, there isn't usually much energy at the upper bandwidth limit, and so any aliasing that does occur will be very low level, and probably lost in the acoustic noise floor -- and in the majority of cases, this 'bodge' actually works out perfectly acceptably.

However, there are a couple of situations where it can cause problems, and these are when recording sources with strong ultrasonic outputs and peaking the levels very high. Such sources will include close-miked brass instruments, close-miked stringed instruments, close-miked cymbals and snare drums... and things like that.

Cymbals and snares drums aren't actually much of an issue as they generate an essentially noise-like signal. So any aliasing that does occur just produces more noise. Of course, the original and aliased noise will have small tonal differences, but most wouldn't notice any significant change and many might even like the effect!

In the case of strings and brass, though, the aliased components won't have the correct harmonic structure and so inherently sound wrong -- and even very low levels of aliasing can be recognised as a form of distortion.

So, in those pretty specialist situations -- I very rarely find myself sticking mics down the bells of brass instruments, or close-miking strings -- I find it better to work at 96kHz and then employ a decent software sample rate converter that applies the correct anti-alias filtering (I use iZotope's RX SRC) as post-production process after completing the mix.

Hope that helps understand the reasoning!

H
User avatar
Hugh Robjohns
Moderator
Posts: 21963
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound

Re: Digital I/O for Edirol UA-101?

Postby BillB » Thu Aug 17, 2017 11:26 am

Thanks Hugh, another 'reference posting' :)

I thought I would round out this thread with what i actually did and what I found in use.

I ended up purchasing a Sony MDS-S707 on ebay, about £30. It's one of their smaller bookshelf units with audio and digital I/O and a similar set of control options to the larger models. I just didn't have room for the full-size types (JE-520 etc). This sits very nicely under the UA-101.

The units are linked together by optical spdif in and out. If the UA Digital In button is engaged, the Sony MD signal will be received and the UA-101 sample rate will be slaved to the Sony, with no obvious digital interference.

If the UA Digital In button is not engaged but the Optical In is still connected, there is a slight whine at high volume (headphones fully turned up). This disappears if Digital In disconnected or Sony turned off.

If the Sony is set to record/monitor (press rec while disk is out) AND Digital In button engaged on UA, much more obvious whine is present. Sort of digital feedback, but quite restrained!

So...
If recording, from UA to Sony, I turn off UA Digital In and/or disconnect Optical In to UA. When playing back from Sony to UA, engage Digital In. Generally, I keep the Sony on standby/off.

Original aim of quickly capturing noodlings without PC is achieved, and I can run a signal from the MDS line out to another recorder if needed. Old school, but I like it.

Thanks all for your help and info :)
BillB
Frequent Poster
Posts: 521
Joined: Mon Apr 07, 2003 12:00 am
Location: East Yorkshire

Re: Digital I/O for Edirol UA-101?

Postby ef37a » Thu Aug 17, 2017 11:46 am

Ooo! Proper job. I wonder if there is such a thing as an HDMI to S/PDIF 'sniffer'? That would mean I could grab radio proggs without the laptop or using my Freeview HDD recorders.

I shall start the search!

https://www.amazon.co.uk/AGPtek-SPDIF-E ... B00ICF4LSC

Ordered, will report back.

Dave.
ef37a
Jedi Poster
Posts: 9574
Joined: Mon May 29, 2006 12:00 am
Location: northampton uk

Re: Digital I/O for Edirol UA-101?

Postby BillB » Thu Sep 06, 2018 6:02 pm

Hi folks, I'm digging up an old thread because I have a continuing story. All that has gone before is probably relevant.

I have inherited a Boss GT-6, which I am more impressed with than I expected, expecially the stereo chorus / phaser settings which sound fabulous on synths. The GT-6 has SPDIF coax out, so I reasoned that anything I was putting through it (mono in only) could have a fully digital (no earth loop) signal path into the UA-101 optical in, provided I insert a coax to toslink convertor.

What I am wondering is how much the convertor itself has scope to degrade the digital signal (given all of the foregoing comments about clock jitter etc). In this situation the GT-6 would presumably become the master clock, but my assumption is that any convertor would be doing a straight bit-for-bit translation from coax to toslink optical. If that is the case, is going cheap an option, for example:
https://www.amazon.co.uk/Tendak-Optical ... 0791YG1X4/
or should I go more pro.... and if so, any contenders? I recall the M-Audio CO2 from way back...

thank you....
BillB
Frequent Poster
Posts: 521
Joined: Mon Apr 07, 2003 12:00 am
Location: East Yorkshire

Re: Digital I/O for Edirol UA-101?

Postby Martin Walker » Thu Sep 06, 2018 7:17 pm

Hi Bill,

I do have an M Audio CO2 converter bought may years ago that's never let me down.

However, as long as that Amazon converter does bit-for-bit transfers (and I see no reason why it shouldn't), that should be fine for your purposes.

The only thing I have spotted is that its power is supplied by a mini USB port, so make sure you have a suitable cable to supply this from another USB device or computer port (my CO2 uses a supplied wall wart).

Good luck!


Martin
User avatar
Martin Walker
Moderator
Posts: 12835
Joined: Wed Jan 13, 2010 9:44 am
Location: Cornwall, UK

Re: Digital I/O for Edirol UA-101?

Postby ef37a » Thu Sep 06, 2018 8:22 pm

I have a couple of "op/coax..coax/op converters that I used to interface an MDisc recorder with a 2496 card. Never a problem.

I took one apart (naturally!) and it consisted of just a hex inverter driving an IR LED so there is no actual "conversion" going on and thus no degradation of the signal is possible AFAIK?

Dave.
ef37a
Jedi Poster
Posts: 9574
Joined: Mon May 29, 2006 12:00 am
Location: northampton uk

Re: Digital I/O for Edirol UA-101?

Postby BillB » Thu Sep 06, 2018 8:48 pm

Thanks chaps, I am reassured by your answers and the simplicity of the circuit as described by Dave. One thought though is that the rise/fall time of the opto-convertors could have an impact - I know you guys will well recall the perils of multiple MIDI In-Thru chains. I think that was around both cumulative delays (which would not apply here as it is one stage only) but also slight signal degradation due to response time.

I wonder if Hugh will be along to tell us “it’s not that simple”

:headbang:
BillB
Frequent Poster
Posts: 521
Joined: Mon Apr 07, 2003 12:00 am
Location: East Yorkshire

Re: Digital I/O for Edirol UA-101?

Postby ef37a » Fri Sep 07, 2018 8:32 am

BillB wrote:Thanks chaps, I am reassured by your answers and the simplicity of the circuit as described by Dave. One thought though is that the rise/fall time of the opto-convertors could have an impact - I know you guys will well recall the perils of multiple MIDI In-Thru chains. I think that was around both cumulative delays (which would not apply here as it is one stage only) but also slight signal degradation due to response time.

I wonder if Hugh will be along to tell us “it’s not that simple”

:headbang:

Not my area of expertize, as you say we need Hugh or Folderol here! However the raw data for the SN74LVCGO4 inverter gives "delta t/delta V" (slew rate?) as 5nS and that is 200mHz, SO far way from 44.1kHz that I really cannot see there being a problem? IIRC analogue power amps only had rise times in the micro second region?

Dave.
ef37a
Jedi Poster
Posts: 9574
Joined: Mon May 29, 2006 12:00 am
Location: northampton uk

Re: Digital I/O for Edirol UA-101?

Postby BillB » Fri Sep 07, 2018 8:49 am

Not your area of expertise, but a persuasive argument just the same!

It occured to me that I was over-thinking the problem and besides, comparing the issue to 1985 opto-isolator technology is probably a bit silly. I think I'll just buy a convertor and see what happens.

Thank you for your thoughts - much appreciated. 8-)
BillB
Frequent Poster
Posts: 521
Joined: Mon Apr 07, 2003 12:00 am
Location: East Yorkshire

Re: Digital I/O for Edirol UA-101?

Postby James Perrett » Fri Sep 07, 2018 2:21 pm

One of these days I'm going to get one of those convertors just to see if it will convert ADAT optical to co-axial and back. It would be really useful to do this because I could then use my BNC patchbay for ADAT as well as SPDIF.
User avatar
James Perrett
Moderator
Posts: 7609
Joined: Mon Sep 10, 2001 12:00 am
Location: The wilds of Hampshire
JRP Music - Audio Mastering and Restoration. JRP Music Facebook Page

Re: Digital I/O for Edirol UA-101?

Postby ef37a » Fri Sep 07, 2018 2:32 pm

James Perrett wrote:One of these days I'm going to get one of those convertors just to see if it will convert ADAT optical to co-axial and back. It would be really useful to do this because I could then use my BNC patchbay for ADAT as well as SPDIF.

AhA! I asked this question quite some time ago James and got pretty short shrift!

"ADAT is different protocol, won't work on coax". I went off, tail between but still thinking "digits is digits?" Since the converters basically just tell a LED to flash on and off bloody quickly, what difference does the protocol make?

Then, inside the AI the light must be turned into electrons coz D/A converters can't "see"!

Dave.
ef37a
Jedi Poster
Posts: 9574
Joined: Mon May 29, 2006 12:00 am
Location: northampton uk

Re: Digital I/O for Edirol UA-101?

Postby Wonks » Fri Sep 07, 2018 11:18 pm

'Protocol' is a funny word because (amongst its many other uses) it can mean just software or a software/hardware mix. In this instance, Dave, I think ADAT was referred to in the software/hardware mix sense (really ADAT lightpipe or ADAT optical interface as true ADAT is the magnetic tape format) . So yes, you probably could convert optical to copper and back to optical with the right converters and the right copper connection.

Lots about converting it to copper on the Wikipedia page https://en.wikipedia.org/wiki/ADAT_Lightpipe.
User avatar
Wonks
Jedi Poster
Posts: 6469
Joined: Thu May 29, 2003 12:00 am
Location: Reading, UK
Now even grumpier than Ivan in his heyday.

Previous

Who is online

Users browsing this forum: No registered users