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Re: Quality of CoreAudio SRC
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Re: Quality of CoreAudio SRC


  • Subject: Re: Quality of CoreAudio SRC
  • From: Brian Willoughby <email@hidden>
  • Date: Sat, 16 Feb 2008 17:29:09 -0800

On Feb 16, 2008, at 12:05, Herbie Robinson wrote:
New results are available at http://src.infinitewave.ca/ for CoreAudio and Logic 8.

All of these seem to allow some amount of aliasing, at least compared to the "iZotope 64-bit SRC Steep, No Alias"

I don't see any aliasing in the Leopard sweep. I do see some sort of noise at multiples of 100 Hz in the 1K tone test, but that can't be aliasing unless there was noise in the input signal (which is why I would have liked to see the input signals before SRC). It looks more like truncation modulated by the sampling rate (44KHz + 100Hz).

Check out the transition results, Herbie. Even maximum quality Mastering mode allows signals above 22050 Hz to pass at around -42 dB. It's hard to tell exactly, given the resolution of the graph, but the aliasing is at least louder than -48 dB.


To be fair, it seems that rather few of the SRC implementations perform perfectly in this regard, except for the iZotope No Alias. Merging AMR, Minnetonka AWE, Pyramix, r8brain Pro, Reaper, Samplitude, Secret Rabbit Code (Best Sinc), Sequoia, Sonar, and Sonic HD (Steep) also have no aliasing, but have other shortcomings in tradeoff.

Depending upon your source material, aliasing filters may not be very important or even needed at all, which is why some SRC implementations make it optional.

Can anyone tell me whether G4 and G5 results would be bit- identical? Are there examples of Altivec code which is G5- specific? My assumption is that the PowerPC model set everything in stone before the G4 or G5 implementations, and the only difference would be speed.

I think IBM dropped a couple of instructions, but nothing that affects audio processing.

Thanks! I was about to set up the same DAW on the same OS and pit G4 against G5.


If someone else has Intel Mac, Infinite Wave might appreciate careful results to be submitted. Every SRC output I created was realized on G4 or G5 processors, so we haven't seen whether Intel SSE can beat PowerPC Altivec on any of the quantization noise measurements. I suppose that some of the SRC implementations on the existing chart are Intel only, e.g. Adobe Audition.

Brian Willoughby
Sound Consulting

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References: 
 >Re: Quality of CoreAudio SRC (From: Brian Willoughby <email@hidden>)
 >Re: Quality of CoreAudio SRC (From: Herbie Robinson <email@hidden>)
 >Re: Quality of CoreAudio SRC (From: Brian Willoughby <email@hidden>)
 >Re: Quality of CoreAudio SRC (From: William Stewart <email@hidden>)
 >Re: Quality of CoreAudio SRC (From: Brian Willoughby <email@hidden>)

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