ACID and Synchronization<\/p>\n
Before a specific discussion of how ACID can synchronize itself to the outside world takes place, some concepts must be defined. Three key protocols are used in the absolute time synchronization world: SMPTE Time Code, MIDI Time Code and MIDI Clock. Other clock sources, such as Word Clock, are beyond the scope of this document.<\/p>\n
SMPTE Time Code<\/p>\n
SMPTE Time Code is the standard timing reference for video applications and tape-based audio. It is an absolute time reference measured in “real time”, meaning that any given SMPTE message will tell me exactly how much time has elapsed from a 0 time. The resolution of SMPTE Time Code varies depending on its frame rate. The uses for different frame rates are beyond the scope of this document. The important thing here is that SMPTE is an absolute time reference.<\/p>\n
SMPTE Time Code is rarely used in software applications directly. To utilize SMPTE Time Code, the application would have to write specific commands for every type of hardware card that allowed a SMPTE input. Instead, most hardware cards that allow SMPTE input convert the SMPTE Time Code into MIDI Time Code and use standard Windows API calls to give up that information to any application that asks for it.<\/p>\n
MIDI Time Code<\/p>\n
MIDI Time Code, or MTC, is nothing but a MIDI representation of SMPTE Time Code. It has the same amount of resolution and options for frame rates. Functionally there is nothing different about MIDI Time Code, other than the format by which it passes its data. It too is an absolute time reference.<\/p>\n
MIDI Clock<\/p>\n
MIDI Clock is a timing base that was developed specifically for MIDI sequencers. It is an absolute time reference, but the time is not measured in hours, minutes and seconds. Instead, MIDI Clock is measured by a number of “ticks” from 0. Ticks are a fraction of a quarter note. Because this time reference is based on fractions of a quarter note from zero, the amount of “real time” that elapses from 0 is completely dependent on the tempo of the generating device.<\/p>\n
For example, if a single quarter note elapses at a tempo of 60bpm, the total amount of elapsed “real time” is 1 second. However, if we crank up the tempo to 120bpm, that same quarter note only takes 1\/2 of a second.<\/p>\n
Because of its tempo dependency, MIDI Clock is the perfect synchronization method for two applications whose internal time base is measured in ticks rather that samples or time.<\/p>\n
Now, on to the subject at hand.<\/p>\n
The number one problem with synchronizing ACID to other applications will be dealing with tempo. If you always have ACID generate MIDI Clock for other applications to chase, there will (should) never be a problem. This would allow you to sync “unrelated” material because the chasing application will change its tempo to match ACID’s. Thus, one ACID measure equals one measure in the chasing application.<\/p>\n
Therefore, if I have a sequence in Cakewalk and I want to lay a killer drum groove to it using ACID, I can do so using MIDI Clock. I don’t have to worry about tempo because Cakewalk will chase itself to ACID’s tempo. In this way I can make the tempo anything I want in ACID and the sync between the two applications should be dead on.<\/p>\n
If ACID is going to generate MTC for other applications or hardware, the audio on the slave must be recorded in sync with ACID. Otherwise, there will most likely be drift between the two because of differences in tempo.<\/p>\n
As an example, If I have some tracks on my ADAT and I want to create a killer drum groove to go with it in ACID, I am pretty much screwed. Even if the ADAT was striped with Time Code, I have no idea what its EXACT tempo is or if it changed a little while it was recorded to the ADAT. This means that even if you generate time code from ACID to the ADAT to chase, 00:01:30.25 might correspond to Bar 9 Beat 3 Tick 100 on ACID and Bar 10 on the ADAT — Obviously they are out of sync. This is completely due to the disparity in tempos.<\/p>\n
The inverse is also true. When having ACID chasing to MTC (only available in Acid Pro 1.0 or 2.0), there is only one sure fire way to get ACID to perfectly sync up: Only use non-stretched streaming tracks in ACID, and they must be recorded in sync with the master application in the first place. In Acid Pro 3.0 or later chasing Acid to MTC is no longer available; only midi trigger. For this reason, chasing ACID to MTC is not the recommended way to sync.<\/p>\n","protected":false},"featured_media":0,"template":"","categories":[],"tags":[34239],"storecat":[],"itemids":[18702],"manufacturers":[],"acf":[],"yoast_head":"\n\n\n\n\n\n\n\n\n\n\n\n\n\t\n