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Gear / Technical Help => Recording Gear => Topic started by: Brian on June 01, 2005, 08:11:00 PM

Title: "spike" in a 744t recording *UPDATE*
Post by: Brian on June 01, 2005, 08:11:00 PM
So, Steve Brothers(fobstl) and I recorded a show together recently with his demo 744t.  I transferred the files to my G4 PB at the venue after the show and took the files home with me.  When I analyzed the combined signal(all 4 channels) I noticed a peculiar spike at around 41,560Hz.  It's totally inaudible(at least to my ears on my current playback system) and doesn't seem to affect the recording, but i think it's an issue that should be addressed.  It's my hope that one of you who is already registered at SD support forum will copy this post to that board so that the SD tech guys can look into it.  After Nick Gregory and Charles Fox's recent 722 AD chipset problem I decided that the AD problem might not exactly be isolated to their specific units or the 722's in general.  I believe this could be an AD chipset problem as well, but am not 100% sure at all.  Here is all the pertinent info.

Source: [SBD>XLR's] + [CMC64's>AM Hyperlite XLR's>V2(hpf@50Hz, -6dB/oct)>custom SD XLR-to-miniXLR's}] > 744t
Bit Depth: 24
Sample Rate: 88.2kHz
Transfer: 744t > IEE1394 > G4 Powerbook > IEE1394 > PC
Mastering: Wavelab 5.0

Here is a picture of the spike zoomed all the way out(full spectrum):

(http://i7.photobucket.com/albums/y280/stl-taper/744t_spike_far.jpg)

Here is a picture of the spike zoomed pretty far in:

(http://i7.photobucket.com/albums/y280/stl-taper/744t_spike_closeup.jpg)

Notice in the closup that the spike appears to be a "plateau" instead of spiking a single frequency.  What does everybody think?  Could somebody please post this over to the SD forum and see what they say?  I'm still waiting on my 722 and can't register yet.  Thanks in advance for any and all opinions and thoughts. :)

edit: grammar and such

edit 2: BTW, for those interested in this, i'm going to be gone the rest of the night and won't be able to report back until tomorrow.
Title: Re: "spike" in a 744t recording
Post by: cfox on June 02, 2005, 10:17:39 AM
Could be a possible firewire transfer issue, is the same spike reproduced when the other guy transfered the file...we had a similar problem on a 744 when transferring a crowes show, but a much more pronounced spike...
Title: Re: "spike" in a 744t recording
Post by: nic on June 02, 2005, 10:27:50 AM
are you sure the "spike" couldnt be from the sbd?
Title: Re: "spike" in a 744t recording
Post by: Mic D on June 02, 2005, 10:38:10 AM
are you sure the "spike" couldnt be from the sbd?

That's what I was thinking. You said you noticed the problem after the 4 channels were combined.
Title: Re: "spike" in a 744t recording
Post by: Brian on June 02, 2005, 05:31:59 PM
are you sure the "spike" couldnt be from the sbd?

That's what I was thinking. You said you noticed the problem after the 4 channels were combined.

i thought about that today and am kicking myself in the head for not thinking about if the spike could be isolated to the soundboard or even worse my V2 :-\.  I guess I assumed that the A&H board didn't have that kind of extended badwidth on it's XLR output.  I have another late session tonight so I'll try to look into it as soon as I possibly can.

but Charles' comment still has me thinking it could be the 744t or a FW transfer problem.  Has anybody forwarded this to the SD support forum?
Title: Re: "spike" in a 744t recording
Post by: MattD on June 02, 2005, 05:56:58 PM
It's not an FW transfer problem, this I can assure you. Data corruption usually sounds like static (from changing the order of bits in a file, for example).
Title: Re: "spike" in a 744t recording
Post by: Brian on June 02, 2005, 06:00:55 PM
It's not an FW transfer problem, this I can assure you. Data corruption usually sounds like static (from changing the order of bits in a file, for example).

that's what I thought but i wasn't too sure(as you could tell :) )  thanks for the clarification.

also, I forgot to mention that this particular unit was on 1.37. 
Title: Re: "spike" in a 744t recording*UPDATE*
Post by: Brian on June 06, 2005, 01:25:24 PM
well i was finally able to get around to investigating this more.  the spike is, indeed, only on the SBD signals, but this still doesn't rule out that it could be the XLR line in on the 744t, IMO.  I wish i had the unit in hand to do more tests.  for now though, i'm sure everyone can rest easy that it's not a severe problem to lose sleep over.
Title: Re: "spike" in a 744t recording *UPDATE*
Post by: dmonterisi on June 06, 2005, 02:10:58 PM
really don't think anyone lost a second's worth of sleep over this "issue"  :P
Title: Re: "spike" in a 744t recording *UPDATE*
Post by: Brian on June 06, 2005, 02:37:38 PM
really don't think anyone lost a second's worth of sleep over this "issue" :P

i rock rocks and stuff with my FFT........hey! :D