Which amplifiers have close to zero latency?

Question

I'm a novice. I'd like to route an electric guitar and several keyboards through a computer for effects processing, and out via the same speakers.

I've tried using different home sound systems; but they all seem to add some delay. I think that modern sound systems use digital sound processing for equalizing the audio, which introduces latency (between 20 and 200ms). The surround sound system I tested was the worst. Other stereos were around 20-30ms. When I tested with a guitar amp, the latency was less than 1ms.

What are my options? I'm guessing the only problem is really the amp. Which type of amp should I look for? Maybe something that doesn't have an LCD display would be more likely to provide analog amplifying and therefore low latency?

My budget is ideally around 200-300 USD for a 100-300w system (used).

I've considered:

• JBL LSR305 (2x active speaker, thus requiring no amp)
• JBL Control1 (passive, thus requires a low-latency amp)

The problem with active speakers is that you need to control power separately, and need a mixer for volume and equalizing (all three functions are that normally done by the home stereo amp). Also, signal cable can pick up noise, while passive speakers suffer from frequency response changes due to cable capacitance. Ugh...

METHODOLOGY OF MEASURING LATENCY

Using Ableton, I record while playing the metronome over the speakers. This allows me to measure the time latency, i.e. the delay between the time the computer makes a sound, to when it is captured. When I record directly from a headphone connected to the output of my USB soundcard, the measured delay is as mentioned ~0ms. However, when I use various sound systems, the delay goes up. Nothing is changed except connecting the sound system instead of the headphone. The delay is therefore most definitely from the sound system.

TEST 1: Measuring 0-1ms

PC -> USB SOUND OUTPUT -> HEADPHONE -> MIC -> USB SOUND INPUT -> PC

TEST 2: Measuring 20-30ms

PC -> USB SOUND OUTPUT -> HIFI STEREO -> SPEAKER -> MIC -> USB SOUND INPUT -> PC

Answer 1

Your unavoidable delay consists of analog filter delay, A&D conversion, downsampling filter (which adds a systemic delay larger than the analog filter), buffering, effect processing delay, buffering, upsampling filter, D&A conversion, analog filter delay (if speakers aren't just abused as lowpass filters).

The conversions and filtering will tend to add about 2-3ms of quite unavoidable delay. Speakers with digital input tend not to take significant amounts over their distribution with that. The buffering of such speakers tends to be negligible in contrast to the buffering/delay introduced by a general-purpose computer employed for digital processing (which includes surround processing, by the way).

Usually you have to fiddle quite a bit with ASIO drivers, buffer sizes, interrupt priorities and whatnot in order to reduce latencies appropriately. In contrast, ready-made speakers with digital input cannot afford the luxury of significant delays since they would become unsuitable for most uses short of only listening to recordings (without accompanying movie or live use). Some systems (such as Bluetooth) can mask part of the bad effects by communicating the incurred delays to the source which can then, at least in the case of replay rather than live use, compensate for it by delaying everything else according to the longest delay path or moving ahead of time for the large-delay paths.

One effect may be that pieces are missing at the start of every replay (and live use becomes annoying). However, that really is a noticeable issue only with really cheap hardware.

So in short: basically you should be fine focusing all your efforts on your computer setup. The speaker tends to incur comparatively small and mostly inavoidable delays.