REW and HDMI with ECM8000

Rudy81

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I would like to simplify my connections to use REW but currently don't have a USB mic. My mic is a calibrated ECM8000 that is powered by a Steinberg UR22, connected via USB to my laptop. Is it possible to use this setup properly with HDMI via ASIO4ALL? I got it to work, but the time reference it gave me was way off, on the order of 60ms.



Am I correct in my understanding that you cannot use a loopback reference when using HDMI and ASIO4ALL?



I am trying to avoid having to purchase a new calibrated mic.
 

John Mulcahy

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Where is your loopback connected? If your processor has line outs for the individual channels you could take the reference loopback connection from one of those line outs. Otherwise you could use the acoustic timing reference.
 

Rudy81

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John, Thank you for chiming in. I have always used one of the UR22 channels as my loopback. In my legacy configuration, where the other channel output went to the AVR multichannel analog inputs, I got a time of about 4 to 6 ms. depending on mic position. Which, is correct when looking at physical distance.

I used the same legacy configuration for the HDMI setup, but now the output was via HDMI from the pc. Same loopback I have always used. The issue is that now I got timing references of 60+ ms. I am not sure if that is the nature of using HDMI or some setting is incorrect in REW when using AISO4ALL.
 

John Mulcahy

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Not surprising, there are likely video frame-rate related buffering delays in the HDMI path. There is no guarantee of maintaining sample synchronisation across separate devices (quite likely it will not be maintained) so you need to use the test signal output device to provide the loopback for it to be meaningful.
 

Rudy81

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Makes sense. I began looking at the HDMI option since I am contemplating a new AVR that does not have analog multi-channel inputs. When I get time I will play around with the HDMI and timing with another speaker and see how that works.
 

Geoffrey

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My problem:
Impulse Response reading is unstable and shifting up to a couple ms.
REW Version 5.20 Beta 27
Maybe someone knows what I am facing here, or how to solve it. It is regarding an issue where the IR, or ETC always shifts even if I just repeat measurements.
This never happened in the past, using only analogue through the soundcard, and maybe it is just a software bug.
My assumption is, that it has to do with the fact, that I have two output devices, a USB Soundcard and a Surround Processor connected to the computer via HDMI.
The Surround processor drives the speaker, the Soundcard serves as Microphone capturing device as well as Timing reference output and Input.
Routing is all correct.
HDMI 8 channel out via Asio4all, microphone in via USB Soundcard Channel 1, Timing Reference via USB Soundcard output 2 and looped back to Input 2.
What is interesting is, that I always have a negative timing in IR, obviously due to the Processor DSP throughput.
All Delays and Processing on the Processors is disabled, except the speaker sizes and crossover points and Bass Management.
Processors used, Marantz 8002, Altitude32, Storm.
Why I am asking this, and why I am not using Acoustic timing reference, because I need to align the phase of all woofers and speakers, which is not possible with acoustic timing reference. I need to see the whole system phase response including what the processor does, to get the good phase reading. Right?
Who has had the same issues? And solved it…
 

John Mulcahy

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There is no fixed timing relationship between different devices so your soundcard loopback cannot function to provide a timing reference with that setup.

I need to align the phase of all woofers and speakers, which is not possible with acoustic timing reference
Why not?
 

Geoffrey

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Ascendo CCRM6
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Ascendo SMSG 24
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There is no fixed timing relationship between different devices so your soundcard loopback cannot function to provide a timing reference with that setup.

Why not?
OK, fair enough, then, how do I set this up, that I can measure everything including the Processor?
 

John Mulcahy

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Use one channel (not a sub channel, the speaker it drives needs to have a tweeter) as the acoustic timing reference for all the measurements.
 

Geoffrey

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Pascal
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Ascendo CCRM12
Center Channel Speaker
Ascendo CCRM12
Surround Speakers
Ascendo CCRM6
Surround Back Speakers
Ascendo CCRM6
Front Height Speakers
Ascendo CCRM6
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Ascendo CCRM6
Subwoofers
Ascendo SMSG 24
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Use one channel (not a sub channel, the speaker it drives needs to have a tweeter) as the acoustic timing reference for all the measurements.
So, what you are saying, only acoustic timing reference works. How do I measure and align then the phase of this speaker selected as timing reference, where is this referenced against? And what if I have a speaker with a DSP inside and I make time alignment of all speakers inside the speakers, then, there is always one speaker not aligned, or how do I solve that riddle?
 

John Mulcahy

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Timing is always relative to something, whether that is the signal coming in on a loopback connection or the acoustic timing signal coming from the tweeter of the selected reference loudspeaker. All that is needed is for the reference to be consistent between measurements. There is no riddle to solve.
 
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