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Microphone Month 4


Problems with latency and “non-professional” sound cards in LIVE.

(Extracted from LIVE tutorials http://www.ableton.com/ )

There are two main problems that the user of a “stock” soundcard will run in to: high audio latency and the lack of an additional stereo output for cueing.

Audio latency is the time between the pressing of a button (or the doing of any action that will change the sound) and the time it takes for the sound to audibly change. Because the latency on standard soundcards is often in excess of 150 milliseconds (1000 milliseconds = 1 second), there can be a frustrating lag on any real-time action that the DJ attempts to do. The result is that mutes/unmutes, the switching on/off of effects, and other actions that are very rhythm-sensitive, often sound sloppy.

There are some workarounds for this problem
One way is to reduce the Sample Rate of the audio output. This option can be accessed under Options -> Preferences… -> Audio. The default setting is 44100, which is CD-quality. However, in a noisy club or rave setting one can often get away with setting the Sample Rate down to 31075 without any audible loss of quality. (This is because audio frequencies work in a logarithmic – and not a linear – fashion, but that’s a discussion for another day.) Doing this will decrease the audio latency to what may be a more manageable level.

Reducing the Sample Rate also has the added perk of reducing the speed at which the hard disk has to access the audio data. This can reduce “glitching” caused by the hard disk trying to access too much data at once.

Another workaround to the latency problem is to set the latency to a millisecond length that is the length of half or a quarter of a musical beat. It is pretty easy to determine the proper millisecond amount using this equation:
(60 / Average Tempo in BPM) X 1000 = The amount of milliseconds in one beat

Here is an example using the average BPM (Beats per Minute) for House music, which is 120 BPM:
(60 / 120 BPM) X 1000 = 500, which is the amount of milliseconds in one beat

Then, this number can be halved or quartered – depending on personal preference, and the minimum amount is limited by the minimum latency that the system can attain without glitching. The audio latency can be set by adjusting the Output Buffer slider under Options -> Preferences… -> Audio.

The result of adjusting the latency in this way is that the DJ can initiate all rhythm-sensitive actions a beat ahead, or half-a-beat ahead, and the audible effect will always occur just when it should. This makes a mix sound much “tighter” and more professional.

The lack of a cueing output is the other major problem with using a standard soundcard to DJ. A DJ uses this extra stereo output to listen to audio channels before they are made audible in the master output. The idea behind this is that a new track can be previewed, tempo matched, and set in the correct starting position without the audience having to hear it. The DJ listens to this cue output through headphones; that way only she can hear it.

Some “stock” soundcards have 5-channel surround sound and in some of these cases, the dual-mono audio output that corresponds to the two rear speakers will be recognized by Live as an additional stereo output. In these cases, those rear outputs can be used as the stereo cueing output. However, the rear channels of some surround soundcards will not be recognized by Live. There are various third-party software utilities that can alter the functionality of some of these soundcards, but that procedure will not be discussed here since the procedure varies greatly from model to model.

If using a soundcard with just one stereo output is the only option, there is still a workaround. (Don’t worry, it sounds more confusing than it actually is!) Obtain one of each of these:
(Part A) 1/8″ male stereo -> dual RCA female adapter
(Part B) 1/8″ female stereo -> single RCA male adapter
(Part C) single male RCA -> dual RCA female adapter.
(A standard RCA cable is also needed).
These adapters are readily available at most electronics stores, and should cost no more than $10-15 USD altogether. Utilizing these adapters properly will enable the DJ to have a separate cue and master section with just a two-channel soundcard. Here is the proper procedure:
(Step 1) Insert the male lead of Part A into the (female) output of the soundcard.
(Step 2) Attach the female lead of Part B to the (male) input of the headphones.
(Step 3) Insert the male lead of Part C into the right female output of Part A.
(Step 4) Insert a (male) stereo RCA cable into the female outputs of part C. (These outputs serve as the master audio output, and they go to an input on the main room mixer.)
(Step 5) Insert the male lead of Part B into the left female output of Part A.

Okay! Now, the pan controls on each audio channel can be used to select whether the channel’s audio is sent to the master outs, the cue outs, or both. If a pan control is set “hard left”, the signal for that channel will only be audible in the cue section (the headphones). If a pan control is set “hard right”, the signal for that channel will only be audible in the master section (what the audience hears). If a pan control is in the middle, the signal for that channel will be audible in both the master and cue sections. The only trade-off is that now the set is in dual-mono instead of stereo, but in a club or rave situation this shouldn’t be noticeable.

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