This feature request was implemented in version 3.5.1 so this request can be closed!
A big thank you to PreSonus Software for implementing this request and of course a big thank you to all the people who supported this request.
Very much appreciated!
A brief note
It seems PreSonus altered Studio One's safety buffer This results in the lowest possible ASIO latency because there's no additional buffer between the application and the ASIO buffers (as requested).
When using a buffer size of 128 samples and a sample rate of 44.1kHz, this comes down to an average of 6.6 ms. That's a 30% lower latency than before. With low latency monitoring enabled this will result in a virtual (reference material is delayed) low latency of a small 4 ms.
As you can see in the image above there's a trade off by the removal of the extra safety buffer. The real time audio (so not what is playing back, but what you hear while playing) has a deviation of ~2.2 ms. In this case the latency sometimes is 5.6 ms while the other moment the latency is 7.8 ms. This is an inevitable part of the ASIO technology itself due to buffer changes on real time input. 2 ms however is imperceptible. Fortunately PreSonus added a safety buffer at higher buffer sizes (above 256) because the deviations there can become noticeable then since the buffer cycles become larger.
Read below why this request is still relevant after the introduction of Low Latency Monitoring for instruments in Studio One 3.5 (jump to post)
I would like to request an overall lower real time audio latency when playing virtual instruments in Studio One.
When I play virtual instruments in real time with an ASIO buffer size of 128 samples at 44.1kHz it should take an average time of approximately 6 ms before I hear the sound after a MIDI trigger is received by the host (ASIO I/O buffers / Sample rate = 128 + 128 / 44.1 = 5.8 ms). However in Studio One it takes an average of 9.7 ms before I hear the actual sound in real time after the MIDI trigger is received. Almost 10 ms really is very long for an ASIO buffer size of 128 samples and a sample rate of 44100hz. I've ran some latency tests across several hosts and Studio One was almost twice as slow as the most responsive host.
MIDI trigger receive (MIDI In) --> Bitwig + VSTi --> Sound (RT VSTi Audio) = 4.7 ms (average)
MIDI trigger receive (MIDI In) --> Cubase + VSTi --> Sound (RT VSTi Audio) = 5.5 ms (average)
MIDI trigger receive (MIDI In) --> Digital Performer + VSTi --> Sound (RT VSTi Audio) = 6.5 ms (average)
MIDI trigger receive (MIDI In) --> Reaper + VSTi --> Sound (RT VSTi Audio) = 7.6 ms (average)
MIDI trigger receive (MIDI In) --> Studio One + VSTi --> Sound (RT VSTi Audio) = 9.7 ms (average)
Notice how consistent Studio One's MIDI and Audio (and their relation) are, but also notice at what huge latency trade-off compared to Cubase (without ASIO latency compensation, which would improve it even further). Bitwig goes even lower but unfortunately the notes in Bitwig aren't placed where they are actually played, so there's a compensation made to the MIDI events afterwards.
Additionally I think most of us are familiar with the phenomenon notes are recorded ahead of time in Studio One. This is because the musical data is extremely accurate. So when you hit a key the musical data (MIDI) is recorded instantly. However the actual sound will take approximately 10 ms with an ASIO buffer size of 128 at a sample rate of 44.1kHz. So in order to get the sound on the right spot when playing in real time (without IQ), you have to play 10 ms earlier. Causing the note to be registered 10 ms earlier. However on playback that 10 ms is compensated and so what you recorded, sound different when you play it back. This is why the lowest possible latency is important, so the human compensation will be minimal.