FORUMS: list search recent posts

Question for Ty

COW Forums : Audio Professionals

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
Steve Wargo
Question for Ty
on Dec 9, 2006 at 5:38:41 am

Ty,

We shoot $250K features with a Sony F-900 and need to bring our audio gear up a notch. What we want to do is record 8 channels of audio along with our HD-SDI during the shoot. We're presenty using a PSC Alpha Mix, Sennheiser 416T and various other mics, going to the camera and an external device, DAT or HDD.

What we'd kind of like to do is run the audio into a rack mounted 8 channel mixer and then run it into a Black Magic Design Multibridge, possibly using the AES-EBU inputs. This isn't for all the time but mostly for interiors. We know that we need power but we need power to run the Mac anyway. We might also need power for other things, like lights.

There are two reasons for this: First of all, we want to capture our HD footage uncompressed. The downside is that Final Cut is only 48k. Not being and audio ace myself, can you explain the sound quality problems between 48K and 96K, which our camera records?

Thanks in advance,

Steve Wargo
Tempe, Arizona

It's a dry heat!


Return to posts index

Ty Ford
Re: Question for Ty
on Dec 10, 2006 at 5:27:00 pm

Hi Steve.

I frequently find myself mixing levels during takes to get the best sound. Will a rack mounted mixer give the sound op the flexibility to adjust levels with adequate ease?

I'd suggest you try Boom Recorder Software with the compatible hardware interface of your choice. http://www.vosgames.nl/products/BoomRecorder/compatibility.shtml

Boom Recorder records poly files. That's a .wav file with up to 8 tracks in Pro Tools LE and significantly larger number in Final Cut Pro. I did 18 because that was the limitation off my I/O box. One file imports really nicely into FCP and put all of the audio on separate tracks.

I'm not necessarily a fan of 96 kHz audio. If correctly designed, 96 kHz offers an extended audio frequency response at the price of doubling your disk space consumption. It also allows the recording any super high audio frequencies (which by the way you'd have to be a dog to hear). The functional argument in favor of 96 kHz is that it allows more gradual decline of the HF filters that must truncate any audio before it reaches the specific sample rate.

The approximate frequency response for 48 kHz, is just under 24 kHz. Most people have a hard time hearing 15 kHz. What CAN happen is that in an effort to truncate frequencies above 24 kHz, the electronic filters can create anomalies that end up in the audible (20 Hz to 18 kHz) range. So shift the sample rate to 96 kHz and operate those filters more gradually and fewer audible artifacts (if any) will be created.

Do we really benefit from a system that lets us have a 20 Hz to 48 kHz frequency response? There are analog and digital circuits that can pass frequencies that high. I'm not so sure we have any amplifiers and speakers that can pass those higher frequencies with accuracy that are affordable to the average home theater system owner.

I may be wrong, but I don't think TV stations, network trunks and satellites have data paths wide enough to handle un compressed 96 kHz. Dolby Digital 5.1 is what, 384 kbps?

A stereo channel of uncompressed 44.1, 16-bit is just under 1.5 mbps.

Here's another, longer explanation of the sample rate/frequency reponse thing.

http://www.digitalprosound.com/Htm/SoapBox/soap2_Apogee.htm

How that?

Regards,

TyFord

Ty Ford's "Audio Bootcamp Field Guide" was written for video people who want better audio. Find out more at http://home.comcast.net/~tyreeford/AudioBootcamp.html
or http://www.tyford.com


Return to posts index

Ray Palmer
Re: Question for Ty
on Dec 11, 2006 at 2:37:27 am

Ty's reply is exactly why I Love the Cow!
What a wealth of knowledge and I learn something almost every day.
Thank you Ty for volunteering your support to the rest of us.


Ray Palmer, Engineer
Salt River Project
Phoenix, AZ
602-236-8224 office
There are three types of people in this world, those that can count and those that can't.


Return to posts index


Ray Palmer
Re: Question for Ty
on Dec 11, 2006 at 2:37:27 am

Ty's reply is exactly why I Love the Cow!
What a wealth of knowledge and I learn something almost every day.
Thank you Ty for volunteering your support to the rest of us.


Ray Palmer, Engineer
Salt River Project
Phoenix, AZ
602-236-8224 office
There are three types of people in this world, those that can count and those that can't.


Return to posts index

Steve Wargo
Re: Question for Ty
on Dec 11, 2006 at 8:05:19 am

Thanks Ty. However, we were looking for an AES/EBU output because want o feed an Apple tower with a Black Magic Multibridge Extreme. The inputs on the multibridge are HD-SDI, Analog dual XLR, and AES/EBU on a 25 pin. http://www.blackmagic-design.com/products/multibridge/specs/

Thanks also for the info on the 48K vs 96K audio. I've had directors tell me that they can't work in anything but 96k and now I know the difference. Final Cut maxes out at 48k.

One unit we're considering is the Presonus DigiMAX. It's 8 channels of AES/EBU and we would use the FCP mixer for the levels.

Your opinion on the DigiMAX?

Steve Wargo
Tempe, Arizona

It's a dry heat!


Return to posts index

Steve Wargo
Re: Question for Ty
on Dec 11, 2006 at 8:24:36 am

[Steve Wargo] "we would use the FCP mixer for the levels. "

We would use the on-screen FCP meters to monitor the levels, not to control them. Just to clarify.



Steve Wargo
Tempe, Arizona

It's a dry heat!


Return to posts index


Will Salley
Re: Question for Ty
on Dec 12, 2006 at 1:23:42 am

I have the DigimaxLT, which is only 48k@ 8 tracks with the optical out. The standard Digimax IS 96k capable and would be the one you want. The mic pres sound quite good and I assume the two models use the same type.

System Info - G5/Dual 2 - 10.4.8 - QT v7.1.3 - 8GB ram - Radeon 9800Pro - External SATA Raid - Decklink Extreme - Wacom 6x8



Return to posts index

Ty Ford
Re: Question for Ty
on Dec 16, 2006 at 4:54:31 am

Hi Steve and folks,

Sorry, I've been smacked with a home construction project, (new room, new roof, new split HVAC) and trying to find honest answers about a mole richardson biax-4 lighting kit I eventually threw down for. My research indicates that there are NO lighting retailers in the DC, Baltimore area worth spit and B&H tried to jerk me around. I called M/R and asked for a GOOD retailer and was directed to Barn Door in CT. So far, so good.

The 96 kHz thing --- for me, unless you are doing something really special and will be delivering in a format capable of reproducing it, is more of a "because we can" issue, especially when (or if) you're delivering on DVD.

The bit depth is more critical. Lest we forget, CDs are 44.1 kHz, 16-bit, but that's a delivery format, not a production or postproduction format. Using 24 or 32-bit to record and mix is where I'd out my storage and processing money. There's a pretty big difference between 16-bit and 24-bit. Actually, a big difference between 16-bit and 20-bit.

The quality of your digital audio is directly proportional to the quality of your analog to digital conversion. I don't have good skinny on the PreSonus DigiMax's A/D converters. The question is whether the A/D converters in the multibridge are any better. If they ARE, then why not just run analog to them?

I use an eight channel A/D converter from a german company, RME to front end my digital audio workstation. I got it years ago to "front end" my small DIGI001 Pro Tools system. I also use outboard preamps by GML, Millennia Media and the Aphex 1100. The two channel Aphex 1100 has it's own A/D converter with AES/EBU output.

I found (as I had hoped) that hot-rodding the front end with preamps and A/D converters improved the sound. In studio sound, converting from mic level to line level as early as possible has been shown to improve audio quality because the stronger line level is more immune to emi, rfi and other nasties. So running short mic cables to high quality preamps helps. House clock all of the A/D converters, too.

Is this helpful?

Regards,

Ty Ford

Ty Ford's "Audio Bootcamp Field Guide" was written for video people who want better audio. Find out more at http://home.comcast.net/~tyreeford/AudioBootcamp.html
or http://www.tyford.com


Return to posts index

Steve Wargo
Re: Question for Ty
on Dec 16, 2006 at 5:20:10 am

We plan to use a Multibridge. The input for video is an HD-SDI connection. The input for audio is "4 x inputs on DB-25 for 8 Ch Sample rate converted".

We need to take our mics into a mixer of some kind and it must have an output to a DB-25 connector". So, I guess I'm a little gray on the "4 inputs being 8 channels." Does this mean that it's 4 stereo channels and not 8 discrete audio channels?



Steve Wargo
Tempe, Arizona

It's a dry heat!


Return to posts index


Ty Ford
Re: Question for Ty
on Dec 16, 2006 at 3:21:16 pm

[Steve Wargo] "We plan to use a Multibridge. The input for video is an HD-SDI connection. The input for audio is "4 x inputs on DB-25 for 8 Ch Sample rate converted".

We need to take our mics into a mixer of some kind and it must have an output to a DB-25 connector". So, I guess I'm a little gray on the "4 inputs being 8 channels." Does this mean that it's 4 stereo channels and not 8 discrete audio channels?"



Steve,

I don't know what "sample rate converted" refers to. It's sort of weird hanging out like that, but not unsual for a video box to not be very explicit about audio details.

OK, there's only one DB25 shown on the extreme and it talks about 8 in-8 out. So I'm thinking it needs something like the Apogee cable below.

http://www.bhphotovideo.com/bnh/controller/home?A=details&kw=APAES8IFC&is=R...

That's an Apogee breakout cable. Four AES in and four AES out. Each AES is a pair of channels. You could use a Yamaha mixer, which can be configured with the right I/O cards to feed and receive from the multibridge.

As for the AES 4 channel, 8 channel thing.

The spec for AES is audio in pairs.

My Aphex 1100 preamp has an AES out. In my Pro Tools system, I can designate each side to a different track. If the software of your system is capable of splitting the AES stereo pairs into individual tracks, you should be fine. It may do that with preferences or you may be able to unlink the tracks once you get them in your editing system.

How's that?

Regards,

Ty Ford



Ty Ford's "Audio Bootcamp Field Guide" was written for video people who want better audio. Find out more at http://home.comcast.net/~tyreeford/AudioBootcamp.html
or http://www.tyford.com


Return to posts index

Steve Wargo
Re: Question for Ty
on Dec 19, 2006 at 7:18:22 am

Ty,

I don't know where this phrase came from. [Ty Ford] "I don't know what "sample rate converted" refers to." Anyway, I think I've got it now. AES is stereo pairs, not discreet channels.

I'll do some more homework. Thanks for the head start.





Steve Wargo
Tempe, Arizona

It's a dry heat!


Return to posts index

Take Vos
Re: Question for Ty
on Dec 20, 2006 at 2:05:01 pm

Hello Ty,

I have done some research in sample conversion and found the following gem. You virtually get a higher bit depth when recording at a higher sample rate (if the AD converter keeps its absolute accuracy at higher sample rates). In the 80's we would have called this oversampling.

Imagine the following four samples recorded at 192 kHz.
0.00, 0.25, 0.50, 0.75

If this gets naively down converted to 96 kHz you get:
0.125, 0.625

If it gets down converted to 48 kHz you get:
0.375

Each sample rate conversion step, gains you one bit of precision.
Actually 24 bit AD converters do this internally, they sample at a high sample rate at low bit depth and then down converts the sample rate.

In principle you don't have to down convert at all, you can send 192 kHz to the speakers and the analogue filters and mechanical limitations would do the sample rate conversion for you.

Cheers,
Take Vos
developer of Boom Recorder


Return to posts index


Ty Ford
Re: Question for Ty
on Dec 21, 2006 at 3:20:14 am

[Take Vos] "I have done some research in sample conversion and found the following gem. You virtually get a higher bit depth when recording at a higher sample rate (if the AD converter keeps its absolute accuracy at higher sample rates). In the 80's we would have called this oversampling.....

Each sample rate conversion step, gains you one bit of precision.
Actually 24 bit AD converters do this internally, they sample at a high sample rate at low bit depth and then down converts the sample rate.

In principle you don't have to down convert at all, you can send 192 kHz to the speakers and the analogue filters and mechanical limitations would do the sample rate conversion for you."


Hi Take,

Right, but as I said earlier, given the limitations of human hearing and the accuracy and bandwidth of playback systems, the reason to go there is not compelling enough for me to go for it on any regular basis, other than "because we can." If you have a VERY, VERY high end project that will benefit from it (and broadcast or DVD distribution doesn't warrant it) then fine.


Regards,

Ty Ford



Ty Ford's "Audio Bootcamp Field Guide" was written for video people who want better audio. Find out more at http://home.comcast.net/~tyreeford/AudioBootcamp.html
or http://www.tyford.com


Return to posts index

Take Vos
Re: Question for Ty
on Dec 21, 2006 at 9:36:57 am

Hi Ty,

I guess you are right, I mean most people think mp3 files are CD quality.
As for "because we can" argument, right now HD-DVD offers (lossless compressed) 5.1 surround 24 bit / 96 kHz. And most new consumer amplifiers can handle this now as well (it is in the HDMI standard).

And I guess high frequency recording is nicest for people creating special effect, who routinely slow down recorded audio to design interesting sounds.

Cheers,
Take


Return to posts index

Take Vos
Re: Question for Ty
on Dec 21, 2006 at 9:39:37 am

Hi Ty,

I guess you are right, I mean most people think mp3 files are CD quality.
As for "because we can" argument, right now HD-DVD offers (lossless compressed) 5.1 surround 24 bit / 96 kHz. And most new consumer amplifiers can handle this now as well (it is in the HDMI standard).

And I guess high frequency recording is nicest for people creating special effect, who routinely slow down recorded audio to design interesting sounds.

Cheers,
Take


Return to posts index


Proper Modulation
Re: Question for Ty
on Jan 8, 2007 at 5:55:12 pm

There seems to be an element of confusion going on in the A/V world right now about 96K audio, which no thanks to Digidesign's marketing dept, many people consider 96k to be "Hi-Def" audio: a technical spec that needs to be married with Hi-Def picture. It's not. 96k is 96k. It's has nothing to do with HD picture. You can still edit in HD in 48, 44, or even 32. Frankly, unless you are a Lakeland Terrier, I don't see why you'd need/want to capture in anything higher than 48K. I'd be very curious as to why that director feels he needs to capture on-set audio at 96k (assuming the reason is legit and not just ill-informed techno paranoia)



Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2017 CreativeCOW.net All Rights Reserved
[TOP]