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Author Topic: Sample Rate  (Read 2426 times)

imitation

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Sample Rate
« on: January 15, 2006, 08:02:21 am »
If  I select 24/96 in DSP studio does MC tell my sound card ( via ASIO x-fi in audio creation mode ) to up sample in hardware or is MC doing the sample rate conversion?
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imitation

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Re: Sample Rate
« Reply #1 on: January 17, 2006, 07:41:51 am »
The reason I ask is my CPU usage goes up to 20% if I chose 96hz in DSP studio. The re-sampling is being done in hardware by the x-fi why does the CPU usage go up to the same level as if I told MC to resample a 48hz wave out signal. If I set same as source in MC, it kicks the sound card back to 44.1hz. So it is using ASIO to communicate directly with the soundcard. It just appears to be re-sampling an already re-sampled signal.
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Matt

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Re: Sample Rate
« Reply #2 on: January 17, 2006, 08:50:17 am »
DSP Studio uses a high quality software resample.  It doesn't depend on the hardware. 

One of the reasons to have a software resample is to avoid the lower quality hardware resamples that are common. 

It's debatable whether resampling to 96 khz helps the quality if you already use a good DAC and a soundcard that can run its clock at 44.1 natively.
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Matt Ashland, JRiver Media Center

imitation

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Re: Sample Rate
« Reply #3 on: January 17, 2006, 05:45:02 pm »
I’m not sure I understand, are you saying if MC receives a 96hz signal it assumes its from inferior hardware and re-samples it again to 96hz? What is the ”same as source” option and why does it switch the soundcard back to 44.1hz? Is there anyway to get MC to just play the sample rate you give it is what I want to know?
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Alex B

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Re: Sample Rate
« Reply #4 on: January 17, 2006, 06:13:23 pm »
Quote from: imitation on January 17, 2006, 05:45:02 pm
I’m not sure I understand, are you saying if MC receives a 96hz signal it assumes its from inferior hardware and re-samples it again to 96hz? What is the ”same as source” option and why does it switch the soundcard back to 44.1hz? Is there anyway to get MC to just play the sample rate you give it is what I want to know?

The setting "Source sample rate" does not alter the sample rate. It sends the audio at the original sample rate to the selected audio device using the selected output mode.

What is your source? Have you ripped high resolution audio discs (like DVD-A) at 96 kHz or is it something else?

If your sound card switches to 44.1 kHz it probably means that it selects the correct sample rate according to the source. You cannot change the source sample rate with the soundcard. It is the last item in the signal chain before the output connectors.
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imitation

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Re: Sample Rate
« Reply #5 on: January 17, 2006, 06:45:49 pm »
Quote from: Alex B on January 17, 2006, 06:13:23 pm
If your sound card switches to 44.1 kHz it probably means that it selects the correct sample rate according to the source. You cannot change the source sample rate with the soundcard. It is the last item in the signal chain before the output connectors.

Understood.

Is there any way to over sample using the x-fi hardware without MC over sampling again in software?
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Alex B

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Re: Sample Rate
« Reply #6 on: January 18, 2006, 06:18:23 am »
The signal path is like this:

Audio file (or CD etc) -> the software decoder that MC uses -> any kind of DSP in MC, including the internal volume and cross-fade (all DSP can be disabled in MC) -> MC's output  -> the soundcard driver.

Your x-fi card is not involved in this path before the signal is out of MC. I really think the sample rate display you are seeing displays the sample rate of the signal that sound card receives. Your sound card may have hardware resampling options that can be enabled in the card's control panel. MC has nothing to do with that and there is no way MC could change resampling that happens after MC in the sound card hardware.

Here is a nice test of the Sound Blaster X-Fi XtremeMusic card: http://techreport.com/reviews/2005q4/soundblaster-x-fi/index.x?pg=1. The test may contain useful information.
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imitation

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Re: Sample Rate
« Reply #7 on: January 18, 2006, 08:38:45 am »
Quote from: Alex B on January 18, 2006, 06:18:23 am
Your x-fi card is not involved in this path before the signal is out of MC. I really think the sample rate display you are seeing displays the sample rate of the signal that sound card receives. Your sound card may have hardware resampling options that can be enabled in the card's control panel. MC has nothing to do with that and there is no way MC could change resampling that happens after MC in the sound card hardware.

That’s what ASIO is for; it allows the software to control the hardware. The only way MC will allow the x-fi to up-sample is if it up-samples first. Whatever sample rate I set in MC as soon as playback starts it changes the sample rate in hardware. If that sample rate is higher MC unnecessarily up-samples when it should just send a 44.1hz signal to the card and tell the card to do it. I want to take advantage of up sampling in hardware with no CPU overhead.

From your link:

"Designed for would-be producers and musicians, the X-Fi's audio creation mode may be the least popular of the three. In this mode, the X-Fi supports ASIO at 24 bits and 44.1, 48, 88.2, and 96kHz with no CPU hit. According to Creative, ASIO 2.0 latencies are as low as one millisecond.

Audio creation mode also supports 3D spatialization for MIDI, allowing for multi-channel MIDI creation. The mode allows up to eight hardware-accelerated effects to be applied to any audio stream moving through the card, and 24-bit sound fonts are also supported. Users are even given some control over the X-Fi's SRC; the X-Fi's internal sampling rate can be switched between 44.1, 48, 88.2, and 96kHz, and users can enable a bit-accurate playback mode that bypasses the SRC, the 24-bit Crystalizer, the equalizers, and the card's smart volume management features."
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Matt

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Re: Sample Rate
« Reply #8 on: January 18, 2006, 10:23:55 am »
You can't open a 96 khz pipe and feed 44 khz data with ASIO.

If the soundcard has special upsampling, it'd need to be a driver setting.  However, it probably doesn't have this.

The job of a DAC is to turn any digital signal into the best possible analog signal.  Upsampling before hand isn't necessary unless you have a fixed clock or bad DAC. (which your card shouldn't have)
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Matt Ashland, JRiver Media Center

imitation

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Re: Sample Rate
« Reply #9 on: January 18, 2006, 07:30:05 pm »
Yes the X-Fi can upsample and it is controlled by the driver.

”The X-Fi's processing power is divided between five internal units: the sample rate converter, digital signal processor, and mixer, filter, and tank engines. Much of the X-Fi's muscle ripples through a sample rate converter (SRC) that Creative claims pushes over 7000 MIPS. The SRC is actually made up of 256 individual sample rate converters, all of which tackle sampling rate conversions in the same manner. First, the sampling rate of an incoming audio stream is doubled. Next, a poly phase Finite Impulse Response (FIR) filter is used to produce a sampling rate four times greater than the desired output sampling rate. Finally, the sampling rate is reduced by a factor of four for output. According to Creative, this process is nearly transparent, and any loss in quality during sample rate conversions is miniscule compared to the noise generated by even the best DACs available on the market. If you're not convinced, the SRC can be bypassed when it's not needed.”

I can do it with foobar using kernel streaming. Foobar sends 44.1hz to the X-Fi and it’s resampled to 96hz. CPU usage 2%. You’re right though I can’t tell the difference so I‘m not going to mess with it. 44.1hz bit-matched playback sounds just fine; I’m done tinkering for now.  Thank you for your time :)



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