• Hardware

  • How to get low latency and good audio quality?

Hello, I have been using the Bela with the Audio Expander to get low latency for a while now. The latency is great, but it has noise issues. From the other thread it sounds like the new CTAG is using sigma-delta converters, that while sounding good (low noise) don't have the really low latency I am after.

Do you think there's any hope for me to have low latency and good audio quality? Even if it had just one audio input and one audio output (doesn't have to have analog/digital lines). My expertise is more on software (C++) then on the hardware side.

    Well, the 1ms that the CTAG is capable of would be by many be considered as "ultra-low latency" (in fact it is basically as low as it gets). Unless you have specific applications in mind that would require smaller latencies (e.g.: feedback control), then you should be happy with it for regular audio effects/interactive audio applications.

    What is your target?

    4 days later

    Consider the fact that sound travels through the air at about 1 foot / mSec. So if you are playing an instrument and sitting 4 feet from the speaker, there is 4 mSec of latency already. Given that frame of reference, how low does your latency need to be? From my informal experiments with an FM wireless system, I can say that I start to be bothered by latency at about 15 feet from the speaker (15 mSec) latency. That's TOTAL latency, mind you, but I think that sometimes people get a little crazy about getting low latency. I'm happy with computer based systems that can achieve 5 mSec base latency.

      djzielin Do you think there's any hope for me to have low latency and good audio quality? Even if it had just one audio input and one audio output (doesn't have to have analog/digital lines).

      jandyman I'm happy with computer based systems that can achieve 5 mSec base latency.

      If the requirements are: audio-quality, one channel input, one channel output, latency below 5ms, then both the Bela/BelaMini (with mic in and headphone out) and CtagFace(with line in/line out) match these requirements (actually exceed them, in that the roundtrip latency can be as low as 1ms).

      jandyman Given that frame of reference, how low does your latency need to be?

      You may find this interesting: https://qmro.qmul.ac.uk/xmlui/handle/123456789/12479

            jandyman but I think that sometimes people get a little crazy about getting low latency. I'm happy with computer based systems that can achieve 5 mSec base latency.

            unfortunately i think this is only partially true. my experience as a musician is different. first and foremost if you play a "real" instrument like a bass or a guitar for example you get tactile feedback and vibrations from the instrument itself, and if it is an acoustic instrument even sound. this makes latency compensation easier for the brain. if you play on a synth though and only hear the sound, low latency is much more important (at least for me)

            another example would be in the studio. a latency above 2ms on the headphones is not possible for me and many musicians i know.

            so it really depends on the instrument and the circumstances. and it is one of the nicest experiences to play a synth with very low latency and getting the impression that the instrument is reacting immediately, it feels much more natural then with a little latency...

            so let's go crazy about low latency :-)

              In terms of want vs need, do I truely need submillisecond latency? Probably not. Do I want submillisecond? Absolutely.

              I already have it with bela plus audio expander. Just the noise is a bit high.

              So my question is if a new board was made that had a higher quality SAR ADC and a higher quality String DAC could I have both extremely low latency and low noise?

              The SAR ADC and the string DAC are fairly high-end: 16 bit, high sampling rate. The mediocre noise performance are a design characteristic of the technology, rather than a defect of the parts in use. These converters are designed for low latency, but cannot provide the low noise typical of oversampled, digitally filtered Sigma-Delta converters.
              This may help to shed some light: https://www.ti.com/europe/downloads/Choose%20the%20right%20data%20converter%20for%20your%20application.pdf .

              Would R-2R get beter noise performance?
              It looks like analog devices makes a couple, AD1866, AD1851, AD1856.

              I am not familiar with those, but it seems that they have no internal filtering, and therefore no inherent latency (except maybe one or two samples due to the I/O registers). However, external filtering is needed, and that will have its own latency.

              Another alternative to reduce latency on many sigma-delta converters is to increase the sampling rate: often the delay in samples is fixed for a given part, therefore higher sampling frequencies will reduce the incurred time delay.