1

What would cause an amp to all of a sudden start sending a signal at a higher pitch and a faster speed?

The System:

Base System
Dell PC w/ SFX 5.60 build 24 -> echo gina 24/96 -> a&h wz14:4:2+ ---

Amps
---> mackie fr series m1200 -> 2 ev sx300's
---> mackie fr series m800  -> 2 apogee acs-1's
---> DBX 1231 Graphic EQ (functioning as a gate for freq. below 100hz) -> tapco j1400 -> JBL SR4725

Everything has worked just fine. I played an effect that comes through all 5 speakers and it sounded fine. I stopped it, adjusted volumes in SFX, then replayed and the sound was out of sync. After a lot of system testing, the mackie m1200 seems to be sending the signal at a faster rate and at a higher pitch than the others. This literally happened out of know where without anyone touching the amps or system configuration.

Any insight into what is happening would be wonderful. Thanks.

2

Both of your Amps have the same power source and share the same common ground?

May be this sound dumb, but have you check that the change in the pitch don't occurs in your D/A Stage.

Instead of relay on the panner of a software, use Dolby white noise audio file in mono and change the output. Check if you hear any change over the outputs and change the amps for double check.

Good Luck

  • Thank you. Yes they all share a power source and common ground. I am not sure what you mean by 'D/A Stage' but I have switched the outputs and inputs between the amps and the problem follows the mackie m1200. The two apogee's on the mackie m800 and the sub on the tapco are in sync in my initial setup but when I put the apogee's on the mackie m1200 and the ev's on the m800 then the ev's and the sub are in sync. I'm fairly certain from this that it is the amp but I don't know what would cause an amp to behave this way so suddenly. – MGriggs Jan 22 '11 at 5:02
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Thank you Alejandro for your response. After several days of troubleshooting and I think I figured out the problem. I hope this might help others in the future.

SFX 5.6 is apparently very temperamental. After testing and testing, the problem seemed to be following the amp, however when I used a cd player to play through all speakers, it was fine. I plugged my ipod into the mixer and ran audio through all speakers and that was fine. I ran audio through SFX again and the problem resurfaced.

Turns out that, out of the 85 files that I had loaded into SFX for my show, 1 of them had a slightly higher bit rate than the rest. However, I hadn't checked this because I wasn't using the file in the show and all the files I was actually using were all the same bit rate and sample rate. I have had problems in the past with SFX doing weird things when all of its files don't have the exact same sample and bit rates, so I deleted the file and poof, like magic, I haven't had a problem since. ...

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