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Author Topic: starting out- some questions about mobile recording and jitter  (Read 3017 times)

dennis1127

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starting out- some questions about mobile recording and jitter
« on: November 30, 2011, 11:11:18 am »

I posted this in the REP forum but the moderator there said I should repost here.

I'm a composition student at Cal State Northridge and I'm just getting involved in starting to record my compositions, so I have some questions. My goal is to make demo recordings of my compositions--that is, I'll get other students to play them either in concert or in a practice room/office, and I'll record them for use in applications and for teachers.

But, I am an experienced audiophile with way the hell too much *Playback* equipment. Also I worked for a while as a programmer and have a degree in electrical engineering. So I know a lot about the technical aspects of digital, formats, some stuff about analog, etc.

I want to have a mobile laptop-based recording setup. I already have an M-Audio Fast Track Pro. It's not high-enough quality for me as an A/D, but it has a S/PDIF input, so I could get another higher quality portable A/D unit with S/PDIF output and send it to my laptop via the M-Audio.

I'm interested in the Apogee Mini-Me, for one.

As far as getting this stuff to work, I think I have the technical know-how, but I have some questions about jitter and digital performance.

First let me say that I have had good success with my playback equipment by using a battery for low-power circuits (such as the DAC) rather than power from the wall. Battery power is much cleaner. I also use a set of parallel capacitors to provide for instantaneous current delivery on transients.

So I want to do something similar with my portable setup.

For the M-Audio Fast Track Pro, I have already tested it like this: I cut the red line in the USB cable to cut the dirty power from the computer, and power it from its 9V input instead (using a 9V battery, or I can also use a 9V linear regulated supply). It works fine.

To consider the Apogee Mini-Me, it can run from a range of inputs from something like 7V to 16V. I already have this nice 12V SLA battery (with the capacitors) so I can use that to power the Mini-Me.

The only connection between the Mini-Me and the Fast Track Pro will be a digital coax (RCA) cable.

Okay, so my question is: is the jitter behavior primary determined by the accuracy of the clock in the Mini-Me? In other words, does the (rather cheap) Fast Track Pro have no influence on the jitter that affects the A/D process, and does it merely have to transcribe the bits?

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Bruno Putzeys

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Re: starting out- some questions about mobile recording and jitter
« Reply #1 on: December 01, 2011, 02:32:20 am »

By the time the analog is converted to digital, it's just data. When recording, jitter added downstream has no effect. In your set-up the ADC's local clock is in charge, the rest slaves via the spdif link. Only the quality of that clock matters. Jitter added downstream will not change the data so you're fine.
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AgusHardiman

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Re: starting out- some questions about mobile recording and jitter
« Reply #2 on: March 10, 2012, 08:11:10 am »

My goal is to make demo recordings of my compositions--that is, I'll get other students to play them either in concert or in a practice room/office, and I'll record them for use in applications and for teachers.
If you need to record more than 2 students at once, you better find audio converter that have minimum of four or more inputs. The Apogee Mini-me is only 2-input. I suggest you look at Presonus Firestudio Mobile or RME Babyface (it's 2-in but can be expanded to 10-in via ADAT & SPDIF).
Maybe you'll think that you don't need more than 2 inputs, but believe me, you do need it later, so if you buy the one that can be expanded, you'll not regret it !
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