"Sorry about the Delay!" - Latency : the Hidden Hazard

Started by Elantric, November 09, 2011, 07:38:33 PM

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Elantric


admin

https://www.bonedo.de/artikel/einzelansicht/foh-tipp-so-bekommt-man-latenzen-in-den-griff.html
FoH tip: This is how you get latencies under control
Professional time management for studio and stage
by Christian Boche


The digital age offers the sound engineer many advantages: Mix scenes are storable ,
https://www.bonedo.de/artikel/einzelansicht/kaufberater-digitalmixer-mit-tablet-und-computersteuerung.html

Total Recall is mandatory. Heavy multicores
https://www.bonedo.de/artikel/einzelansicht/9-simple-tipps-fuers-kabelverlegen.html
are replaced by lightweight network cables, and a flexible signal flow through network protocols such as DANTE and AVB allows the construction of complex systems with little hardware. However lurks in the digital world, a treacherous opponent called latency, which can cause inconvenience through comb filter effects.

Content:

What is latency and where does it come from?
Signal propagation time
Watch out, trap!
External effects
On stage
Measure latencies yourself
What is latency and where does it come from?
In purely analog systems, the signal propagation time from input to output is always 0 milliseconds - current flows at about the speed of light - resulting in the AD / DA conversion and the use of digital signal processors delays in the millisecond range, the so-called latencies.

Signal transit time and RTL
Latency is usually specified in milliseconds for digital consoles. This value describes the time it takes for a signal to go from an analog input to the analog sum output. This process is also called Round Trip Latency, RTL for short. Here are a few RTLs common Digimixer:

Digico SD-7: 2 ms @ 48 kHz
Behringer X32: 0.8 ms @ 48 kHz
Yamaha PM05D-RH: 2.56 ms @ 96 kHz
Yamaha CL5: 1.98 ms @ 48 kHz
By the way, if you increase the sampling rate, the latency will be reduced: If the sample frequency is doubled, the RTL will be halved. However, the significantly increased amount of data significantly burdens the CPU or the DSPs, so that only more expensive digital mixers are often equipped with correspondingly powerful components.


Be careful with the double routing in a digital mixer, especially if external plugins are included

Watch out, trap!
If one considers the latency times of current digital mixers mentioned above, one should actually think that these do not play a significant role in live operation. At a theoretical sound speed of 343 meters per second, 3 milliseconds equals just one meter away. The tricky thing about it: In digital mixing consoles, latencies are by no means static, but vary depending on routing and effects.

Due to different signal propagation times, especially when using more complex routings, this can lead to audible delays and comb filter effects. A first example: The RTL of a Yamaha PM05D-RH is 2.56 milliseconds. If you do not route the signal directly to the sum output, but only via a group or a matrix output, the runtime increases to 3 milliseconds.

This is not a problem for the entire runtime. However: If I put the channel once directly on the sum and in addition over a group on the sum, it comes due to the runtime differences to Kammfiltereffekten. The sound suddenly becomes hollow, slack, and in extreme cases, it sounds as if the guitarist had inserted a phaser or flanger into the mixing console.

Another example: The Behringer X32's built-in Wave Designer effect increases the latency from 0.81 to 2.23 milliseconds. For example, if you want to double-microform a bass drum and then thicken it by parallel compression, you will get a runtime difference between both channels of 1.42 milliseconds. The simplest solution to avoid this difference in the sound gap: You also load the effect in the first channel, but leaves the gain control in the zero position.

External effects
Special care should be taken when integrating external effects via DANTE, AVB or Soundgrid servers: Both the type of integration itself and the external plug-ins can introduce significant latencies. That should not be explored during a gig!

The author once had the glorious idea of ​​using a multiband compressor from FabFilter in the mixer's total. During the soundcheck there was a noticeable latency between the drums from the stage and from the PA. The problem was the look-ahead function, which delayed the input signal by 20 milliseconds. Therefore, general care should be taken with phase-linear EQs, limiters and multiband compressors with look-ahead.

Some professional sessions, such as the Avid-Profile series or the Midas-Pro consoles, offer automatic latency compensation, much like a DAW. Then all relevant channels are delayed to the slower subgroup so that no sound artifacts interfere with the mix result. However, automatic latency compensation increases overall latency, which can be problematic in monitor use.


Even with a Yamaha M7CL, the signal propagation time changes when effects are inserted or signals are routed through matrices

On stage
... there is a real runtime boom: The guitarist is three meters from his amp away (about 10 milliseconds latency), the singer sounds about the floor wedge (1.5 meters = 3 - 4 milliseconds latency), at the same time a little on the Main PA and the sidefills. What damage can the 3 milliseconds of a digital mixer cause?

Well, in a live gig, the digital mixer is rarely the only digital device. Digital radio links, some with DANTE connection, digital stage boxes, digital speaker controllers - all these devices generate latencies that add up in the worst case to an audible overall latency.

While latencies of 10 - 12 milliseconds are basically justifiable when using floorwedges, this looks quite different with an in-ear system. Here, the signal transit times are almost identical, which is why a good in-ear mix always sounds tidier and closer than a classic wedge mix. Too high overall latency is therefore more noticeable in In-Ears. Here is a tip: With a little reverb on the entire in-ear mix, you can convey a pseudo-spatiality that conceals high signal propagation times.

Basically, if you are first in the digital world, you should stay there as long as possible. Too many AD / DA conversions do not make the sound any better and also increase the latency. Most digital consoles and audio interfaces have digital summing outputs (S / PDIF or AES / EBU) that connect to the digital inputs of PA controllers and system power amplifiers. This saves AD / DA conversion and signal processing time.


The Midas Pro2C has some automatic latency compensation options

Measure latencies yourself
If you want to check the latency of your live setup, access audio analysis software like Smaart or SysTune. For the measurement, you only need a two-channel audio interface. The structure is as follows: The output of channel A of the interface is connected to the input of channel A (loopback). This is our reference link.

You connect the output of channel B to an input of the console, while the input of channel B is connected to the output of the mixer. Now the measurement can begin. With Smaart you can read the exact RTL via the Delay Finder. Channel A should not show any delay due to the loopback, channel B informs about the latency of the mixer. A free alternative is the Room EQ Wizard (REW).

Here, too, two-channel reference measurements can be made. Under "Information," REW specifies latencies in milliseconds - a good basis for professional latency management.


With the software Room EQ Wizard the latency of an audio system can be determined by means of a reference measurement


https://www.roomeqwizard.com/

With the software Room EQ Wizard the latency of an audio system can be determined by means of a reference measurement

admin

An important aspect is daisy chaining too many digital devices in series , and understanding that the TOTAL SYSTEM Latency may become much higher than expected, and definitely a battle for a few here

Sources of latency include:

* Wireless Guitar module latency time

* DSP based effects with individual A/D >DSP>D/A conversion latency time

* DSP based effects Patch type - many Drop tuning effects have higher latency than expected

* DSP Based Modeler Specific patches suffer higher latency

* Guitar to MIDI System

* Distance mic'ed speaker cab

* Wireless IEM Monitor

often you reach a proverbial "straw that breaks the camels back" and exposes the "too much latency" issue - which when playing with IEM monitors becomes a dreadful experience for many


Another aspect is Phase Error

If playing guitar into a Y adapter, and one leg feeds a tube amp, while other feeds a DSP Modeler, and both are feeding multiple channels on a pro mix board, Many Pro Mixers (Yamaha) include a variable delay on each channel specifically to "Time Align" the audio sources and correct for Dry / Wet time alignment phase errors   
https://www.soundonsound.com/techniques/studio-sos-fixing-monitor-phase-problems






admin

Good Timing: Manually Compensating For Outboard Gear Latency
February 12, 2020
Michael Reed

When two signals are combining at the same level but with different timing in a bus or a loudspeaker, the result will be comb filtering upon the combination. To avoid this, the two signals must be corrected to arrive in time with each other. Here's a way to do it.



https://www.prosoundweb.com/good-timing-manually-compensating-for-outboard-gear-latency/


gumtown

I'm using a delay on my Yamaha digital mixing desk on the foldback monitors, a few milliseconds,
which seems to help with aligning the monitors and F.O.H speakers more in phase, for a better on stage sound (less mud) and less feedback.
Free "GR-55 FloorBoard" editor software from https://sourceforge.net/projects/grfloorboard/