ASIO401 does not provide a graphical interface (GUI) to adjust its settings. This is because developing a GUI typically requires a significant amount of developer time that ASIO401, sadly, doesn't have. This explains why nothing happens when you click on the ASIO driver "configure" or "settings" button in your application.
Instead, ASIO401 settings can be specified using a
configuration file. ASIO401 will search for a file named
ASIO401.toml directly inside your Windows user profile folder; for
example: C:\Users\Your Name\ASIO401.toml.
If the file is missing, this is equivalent to supplying an empty file, and as a result ASIO401 will use default values for everything.
Configuration changes will only take effect after ASIO401 is reinitialized. Depending on the ASIO host application, this might require the application to be restarted.
The configuration file is a text file that can be edited using any text editor, such as Notepad. The file follows the TOML syntax, which is very similar to the syntax used for INI files. Every feature described in the official TOML documentation should be supported.
ASIO401 will silently ignore attempts to set options that don't exist, so beware of typos. However, if an existing option is set to an invalid value (which includes using the wrong type or missing quotes), ASIO401 will fail to initialize. The ASIO401 log will contain details about what went wrong.
attenuator = false
bufferSizeSamples = 512Boolean-typed option that determines if the QA401 hardware attenuator should be engaged or not.
If the option is set to true, the QA401 attenuator will stay engaged.
If the option is set to false, the QA401 attenuator will be bypassed during
audio streaming.
Note that, contrary to the QuantAsylum Analyzer application, ASIO401 will not adjust sample values in any way to account for the presence or absence of the attenuator. In other words, defeating the attenuator has the effect of adding 20 dB to the samples coming from ASIO401.
CAUTION: do not apply high voltages to the QA401 inputs while the attenuator is bypassed. See the QA401 User Manual for details.
Example:
attenuator = falseThe default behaviour is to keep the attenuator engaged.
Integer-typed option that determines which ASIO buffer size (in samples) ASIO401 will suggest to the ASIO Host application.
This option can have a major impact on reliability and latency. Smaller buffers will reduce latency but will increase the likelihood of glitches/discontinuities (buffer overflow/underrun) if the audio pipeline is not fast enough.
The QA401 device can store up to 1024 samples in the hardware itself.
On the output (playback) side, ASIO401 always keeps one or two buffers inflight at any given time; if the buffer size is larger than half the hardware queue size, the excess data is queued on the computer side of the USB connection and is streamed progressively as space becomes available in the QA401 hardware queue.
On the input (recording) side, ASIO401 always keeps a read request inflight such that the QA401 hardware queue is always being drained, and hopefully stays nearly empty at all times.
At 48 kHz, the best tradeoff between reliability and latency is likely to be 1024 samples; this ensures there is always some data queued on the USB host side to keep the QA401 hardware output queue nearly filled at all times. Smaller buffers only make sense if you care about latency. Larger buffers will always improve reliability and efficiency by relaxing scheduling constraints and allowing for more data to be preloaded, but come with diminishing returns.
At 192 kHz, it is recommended to use a larger buffer size because 1024 samples implies a ~5 ms buffer processing deadline, which is likely too tight for most systems, resulting in discontinuities (glitches).
Note that some host applications might already provide a user-controlled buffer size setting; in this case, there should be no need to use this option. It is useful only when the application does not provide a way to customize the buffer size.
Example:
bufferSizeSamples = 512 # ~10.7 ms at 48 kHzThe default behaviour is to advertise minimum, preferred and maximum buffer sizes of 64, 1024 and 32768 samples, respectively. If the application selects a 192 kHz sample rate, the preferred buffer size becomes 4096 samples.
Boolean-typed option that determines if ASIO401 will fetch audio data from the QA401 for clock synchronization purposes even if no input channels are enabled.
This option only has an effect if the ASIO Host Application exclusively uses ASIO401 in the output direction. The value of this option is ignored if any input channels are used, since in that case ASIO401 has to read data from the QA401 anyway.
If the option is set to true (or the ASIO Host application enables any
input channels), then ASIO401 will use read operations to monitor the progress
of the QA401 clock, and will use that information to issue writes at the
appropriate time. This decreases output latency.
If the option is set to false (and the ASIO Host application does not enable
any input channels), then ASIO401 will not issue any read operations, and will
use write pushback to synchronize with the QA401 clock. This improves efficiency
and relaxes performance constraints because USB load is reduced. On top of that,
the likelihood of glitches (discontinuities) from missed deadlines is reduced
because the QA401 output queue acts as an additional buffer. However, for the
same reason, the output latency is increased by the length of the QA401 output
queue, i.e. 1024 samples.
In general, it does not make sense to enable this option unless you care about latency.
Example:
forceRead = trueThe default value is false.