[Ardour-Users] Ardour/Mixbus 32C adds a background noise

Gunter Königsmann gunter at peterpall.de
Thu Sep 22 12:39:15 PDT 2016

>> Just a shot in the dark, but do you do hardware monitoring or software
>> monitoring in Mixbus?
> 'Record monitoring handled by' is currently set at 'audio hardware'.
> The assumption is that this would be the best way to get a
> responsive real-time feedback, especially when recording guitar playing
> and monitoring through headphones.

It is as it doesn't introduce an additional delay into the audio data
before you can listen to it. But this at the same time means that you'll
hear the noise the amplifier of your audio inputs does produce.

Another possible source for noise lies in the real-time nature of Ardour
and Harrison Mixbus: These programs both prepare only the audio data for
the next millisecond or similar - which enables them to react to input
in next to no time. But it means that the CPU is awaken once per
Millisecond, gets the high-priority task of preparing a Millisecond
worth of audio data - and then goes to sleep again.

When the CPU works it uses loads of energy. When it sleeps it doesn't =>
The input current changes with a frequency in the kilohertz range. As
current always produces an magnetic field this will produce a magnetic
field that changes with a frequency that is in the audible range. Every
wire, pcb line and similar near to it will act as the receiving antenna
for these fields. The question is, though, if the noise is strong enough
so it can be measured and/or heared. Also if you draw current from a
wire the voltage will drop due to its resistance and due to its
inductivity. If you stop drawing current abruptly the inductivity and
the power supply will produce a short voltage overshoot. If your
soundcard or audio interface isn't carefully designed it might "see"
this, too.

In my case if I use good headphones I can hear the CPU working if I use
the internal soundcard of my laptp. But this noise won't arrive in the
tracks I record. If I use my scarlett (USB Audio interface) I won't hear
noise from my Computer safe the fan if the computer is in the same room
as is my microphone.

Kind regards,


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