Home recording - the truth about latencies
Latency is unavoidable when working with digital signal processing:
|Delay||equivalent distance *)|
|A/D converter||0.5 ms||0.17 m|
|D/A converter||0.5 ms||0.17 m|
|Buffering for digital signal processing **)||typically
3.5 - 30 ms
1.16 m - 9.90 m
*) For example as the velocity of sound is approx. 330 m/s, the sound needs e.g. 1 ms to go 0.33 m.
**) for example at a sampling rate of 44.1 kHz and a buffer size of 1024 samples you need at least 1024/44.1 * ms = 23.2 ms to fill the buffer.
... you might think. But: 10 ms is the maximal delay you (I) can handle to exactly hit the metronome beat.
And that also meets my experience on large stages: You have to make sure that no musician is farer away from the drums (and bass) than 3 meters.
Otherwise you´ll not get tight and this can muck up your whole concert. The other instruments can easily be monitored with the nearby monitor speakers.
So that´s what I think about acceptable delays:
|Delay||equivalent distance||Feeling to hit the metronom|
|4.5 ms||1.5 m||Excellent|
|6 ms||2.0 m||Good|
|10 ms||3.3 m||More or less Ok|
|15 ms||5 m||Difficult|
|> 15 ms||> 5m||By no means at all|
What to do?
There are several ways to avoid too great delays:
- Hardware monitoring: Most of the sound cards (even the cheaper ones) have some sort of direct analog recording out you can put through to your head phones. Of course your instrument is then "extra dry" (without any effect)
- The better hardware devices support delay times lesser than 10 ms even if the buffer size is 2048 samples. Don´t ask me how this works, probably with an internal greater sampling and refresh rate. These devices support also some built-in effects such as compressors and equalizers without extending the 10 ms delay.
- Using a mixer between your instrument and the sound card device and split the signal, one to the sound card and the other to your head phones.
Measure the delay - don´t trust the manual!
An easy way to measure the delay works as follows:
Use a separate metronome and record the metronome beat with the 1st microphone
Send the sound to the head phones and record the output with a 2nd microphone (as near as possible).
|Compare the two records: Here we got 4.5 ms delay|