Hi Chris,
I've read a variety of articles mentioning the benefits of a real-time OS for audio quality. Do you echo this sentiment? To what degree do you think it matters?
Best regards,
Gary
From: Chris Rice [mailto:crice@bryston.com]
Subject: Re: real time os
Hi Gary,
It's essentially snake oil, the idea behind a real time OS is to give certain tasks absolute priority for best possible timing. In the case of audio this sounds like a good thing, however it's a non-issue and would only be useful if the CPU running the OS where also directly controlling the analog signal outputting the audio. This is not the case for the BDP or even average desktop computers as they both have sounds cards that handle this task. As for any application towards outputting the data to the sound card, whether that be. A traditional sound card or a USB DAC out BDP is configured to buffer as much data as possible into system memory. There are two buffers and input buffer that is 2KB in size (MPD) and a output buffer that will use as much memory that is available (ALSA). As the songs in the playlist are decoded by the system, the decoded material is then stored in system memory until it's handed off to the sound output device (sound card or USB dac).
Think of a barrel with a small whole in the bottom being filled with water. The water escaping from the bottom of the barrel is the data being sent to the sound output device, the barrel itself is the buffer and the water filling the barrel is the computer reading the data. So if the computer becomes occupied doing another task, the flow slows down or stops all together;
but it's ok because the barrel is still full of water and as long as water remains in the the barrel it will continue to flow out at a constant pace.
If you venture into the BDP's settings page, under services you'll notice some statistics, one of which is system memory. As the playback music, the larger your playlist becomes the memory becomes used. This is the BDP buffering as much audio as possible, however if you skip a song it has to start over.
You can test this by playing some music off of a USB drive, once it has started playing for 15-20 seconds. Pull the thumb drive out and the BDP should continue playing for a few seconds. It would play longer but the BDP is configured to send the stop command once it's realized the drive has been pulled.
Hope this information helps Gary, feel free to email me with any further questions or concerns.
Cheers,
Chris
Embedded Linux Engineer
Web Application Developer
Bryston Ltd.
