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  #1  
Old 07-30-2015, 03:04 PM
Amack Amack is offline
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Default DAW System/Subsystem Performance Evaluation

DAW System/Subsystem Performance Measurement/Evaluation

From my perspective as a recently retired EE, DAW systems are basically data acquisition, processing, playback, and data logging systems. For these types of systems it’s important to understand the limitations of each of their constituent subsystems to achieve optimal performance/results as well as perform meaningful cost/benefit analyses when considering changes.

As pointed out in http://www.rane.com/note145.html, meaningful measurements of “high end” audio equipment used to require the use of very expensive test equipment. Fortunately, that’s no longer true. Likely everyone that participates in this DUC already has all the test equipment they need (their audio interfaces). They likely only need a little background information and some additional inexpensive/free software to make meaningful quantitative measurements.

The link above describes the most common measurements and procedures. The TrueRTA website (http://www.trueaudio.com/rta_abt1.htm) provides both background information and excellent analysis/measurement software for PCs. Audacity http://sourceforge.net/projects/audacity/files/ provides additional (non-real time) analysis capabilities (for both PCs and Macs). http://www.parts-express.com/dayton-...ystem--390-792 is a turnkey system for measuring speaker and listening room performance.

Those that insist that their ears is all they need to judge the performance of equipment might want to check their hearing at http://myhearingtest.net/ (especially the older ones.) Additional useful resources for those wishing to make subjective evaluations are available at http://www.audiocheck.net/ . That link also has on-line generators that can be used to easily produce test signals that can be used with Audacity for quantitative measurements.

http://duc.avid.com/showthread.php?t=368473 describes how to accurately measure system/subsystem latency (delay) and DAW system record latency compensation (RTL) error.

http://src.infinitewave.ca/ (thanks mesaone!) makes it easy to evaluate and compare the sample rate conversion performance of various DAWs.

Amack
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  #2  
Old 08-10-2015, 10:19 AM
Amack Amack is offline
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Default Re: DAW System/Subsystem Performance Evaluation

Here's a plug and play system (PC only) for testing/analyzing speakers and listening room acoustics: http://www.parts-express.com/dayton-...ystem--390-792. TrueRTA (mentioned in post #1) can do some of that as well with a calibrated measurement microphone.
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  #3  
Old 08-21-2015, 06:41 PM
mesaone mesaone is offline
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Default Re: DAW System/Subsystem Performance Measurement/Evaluation

Hi Amack, just a note about the SRC comparison. There is more to consider than just the graphics shown by infinitewave. I'll post my quote below, but here's the short version:

When dealing with material recorded and played back in the real/analog world, some digital shortcomings will be completely eclipsed - for example, the aliasing that is shown in the Pro Tools SRC image referenced below. It is approx -105 dBFS by the time it reaches the range audible by an adult human with "good" hearing (18 kHz). This means it's not only well below the noise floor of most analog equipment recorded to digital at a nominal level (when using 0 VU = -18 dBFS or anything in that range, most analog signal chains has a noise floor above -105 dBFS) but it's also below the truncation point of 16 bit digital audio!

While the SRC is obviously imperfect, real world use renders the imperfections moot. Please understand this, as sound is only in your realm (electrical signals) for half of its journey.

Quote:
Originally Posted by mesaone View Post
Audacity won that shootout. But don't let the graphic fool you, what you see is aliasing starting at -70 dBFS and attenuating rapidly as the frequency decreases. It's at -90 by the time it reaches the audible range, and by the time it reaches 18 kHz it looks to be at a level that will be truncated by 16 bit audio anyway (-96 dBFS). It's a minor difference at most, especially if you take the noise floor of your recording into account. But the difference is there.

What you see is a frequency sweep over 5.25 seconds, from 1 Hz to 22 kHz. This particular graph shows a spectrogram of the result, and the aliasing incurred by the conversion. More info here: http://src.infinitewave.ca/help.html

The image is from http://src.infinitewave.ca/ which compares the sample rate conversion of many programs. It's not completely up to date (latest PT version is 10.3.5) but it's a great resource.
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Last edited by mesaone; 08-21-2015 at 06:51 PM. Reason: clarity
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  #4  
Old 08-21-2015, 07:56 PM
Amack Amack is offline
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Default Re: DAW System/Subsystem Performance Measurement/Evaluation

mesaone,

Thanks - I understand. I really do appreciate you posting that quite useful SRC link! But I still don't understand the magnitude/source of the apparent square wave "high frequency ringing" in the sample rate conversions shown in my latency measurement thread.

Do you know of any other website(s) showing similar measurements for audio interfaces?

amack

Quote:
Originally Posted by mesaone View Post
Hi Amack, just a note about the SRC comparison. There is more to consider than just the graphics shown by infinitewave. I'll post my quote below, but here's the short version:

When dealing with material recorded and played back in the real/analog world, some digital shortcomings will be completely eclipsed - for example, the aliasing that is shown in the Pro Tools SRC image referenced below. It is approx -105 dBFS by the time it reaches the range audible by an adult human with "good" hearing (18 kHz). This means it's not only well below the noise floor of most analog equipment recorded to digital at a nominal level (when using 0 VU = -18 dBFS or anything in that range, most analog signal chains has a noise floor above -105 dBFS) but it's also below the truncation point of 16 bit digital audio!

While the SRC is obviously imperfect, real world use renders the imperfections moot. Please understand this, as sound is only in your realm (electrical signals) for half of its journey.
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  #5  
Old 08-21-2015, 08:48 PM
mesaone mesaone is offline
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Default Re: DAW System/Subsystem Performance Measurement/Evaluation

It's not "ringing" as such, it's unlike the ringing associated with imperfect impulse responses or acoustic resonance. It's called aliasing which is essentially a reflection caused by imperfect Nyquist filters.

http://www.soundonsound.com/sos/jan0...s/qa0106_2.htm

http://www.maximintegrated.com/en/ap...dex.mvp/id/928
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  #6  
Old 08-22-2015, 11:08 AM
Amack Amack is offline
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Default Re: DAW System/Subsystem Performance Measurement/Evaluation

mesaone,

Good links on aliasing - thanks! But I was referring to the test signal digitally generated by Audacity at 192 kHz and imported into Pro Tools at 96 kHz for 'playback" on the first track. Unlike the other tracks, it didn't go through the A-D and D-A process anti-aliasing and re-construction filters.

Amack

Quote:
Originally Posted by mesaone View Post
It's not "ringing" as such, it's unlike the ringing associated with imperfect impulse responses or acoustic resonance. It's called aliasing which is essentially a reflection caused by imperfect Nyquist filters.

http://www.soundonsound.com/sos/jan0...s/qa0106_2.htm

http://www.maximintegrated.com/en/ap...dex.mvp/id/928
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  #7  
Old 08-24-2015, 10:12 AM
mesaone mesaone is offline
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Default Re: DAW System/Subsystem Performance Measurement/Evaluation

Sample rate conversion happens whenever you change the sample rate of recorded material. It is completely different from digital-to-analog conversion (analog audio does not have a sample rate).

If you generate a signal at 192 kHz in the digital realm, and then import to Pro Tools at 96 kHz, there will be sample rate conversion because 96≠192.
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  #8  
Old 08-24-2015, 11:16 AM
Amack Amack is offline
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Default Re: DAW System/Subsystem Performance Measurement/Evaluation

That's my point - I don't understand the "ringing" on the first tracks, since the SRC measurements indicate that there shouldn't be any.

Quote:
Originally Posted by mesaone View Post
Sample rate conversion happens whenever you change the sample rate of recorded material. It is completely different from digital-to-analog conversion (analog audio does not have a sample rate).

If you generate a signal at 192 kHz in the digital realm, and then import to Pro Tools at 96 kHz, there will be sample rate conversion because 96≠192.
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