*DVRex/DVRaptor/EZDV all work the same. I am referring as DVRex but the below explanation applies to every product.

First off, why are we resampling Canon Audio?
The answer is, because we're editing video, not only capturing and playing back on the same hardware.

Our product is targeted to people who edit video on their PCs. And because there are different cameras from different companies, we must support data mixing between different types of cameras. And video captured in camera A and camera B should be able to be mixed, and also video captured in camera A should be able to be edited and then outputted to camera C.

To do this, the audio data within the video file must be arranged to a proper NTSC audio level, to be able to mix and output to multiple systems. The first camera manufacturer that we set as a standard for our system use was Sony. The DVRex was designed to support Sony DV/DVCAM camcorders and also support locked audio in DVCAM systems. For instance, in locked audio format, the audio output must be set to exactly 32032hz per second, otherwise the deck will not accept the audio in sync. The Sony consumer DV cameras are also designed to record/output audio in and around that frequency, averaging around 32032hz for every second.

Then came the Canon XL1. The main problem with this camera was that the audio frequency changed heavily for every second, sometimes with differences of more than 20 to 30hz between adjoining seconds. And the average audio frequency was around 32053hz for every seconds. With this type of audio data, if we capture video from the XL1 as is and then try to mix with clips from Sony cameras or try to output as DVCAM locked audio, the audio sync will be way off, and unusable.

So to support XL1, what we did was this; when capturing, DVRex will look at the first second (store it in the buffer) and measure the sampling rate, and if that sampling rate was outside the range of 32026hz to 32038hz, DVRex will consider the camera as an XL1 and capture audio as 32053hz per second. After sampling as 32053hz per second, it will convert the audio to 48048hz, and then convert back to 32032hz, to create an AVI file. This is to create an AVI file that is compatible with other cameras.

Now, if the audio data is inside the range of 32026hz to 32038hz, DVRex will use the measured sampling rate and capture audio as that sampling rate, and create an AVI file in that audio sampling rate.

After we create a project in RexEdit, the project output will be in exactly 32032hz per sec, no matter what AVI clips you use in the project.

After the support for XL-1, more irregular cameras/decks came in the market. Ones such as the Sony Media Converter, outputted signals above the 32026hz to 32038hz range, but had a sustained frequency for every second. So we added a setting CanonAudio1=3 in the .ini file, which will look at the first second and measure the sampling rate, and DVRex will capture audio in that frequency. And if that sampling rate was outside the range of 32026hz to 32038hz, DVRex will convert the audio to 48048hz, and then convert back to 32032hz, to create an AVI file. 

When the DVRex is doing the process of converting the audio to 
48048hz, and then convert back to 32032hz, "Rec+SC" will show 
in the capture information box in RexVideo.

But, there was one problem with this process. When the audio was 
converted to 48048hz and then put back to 32032hz, high frequency 
noise showed in some situations. To ease the noise, we added a new 
setting in the .ini file, as Cap32to48=1. With this setting, if 
that sampling rate was outside the range of 32026hz to 32038hz, 
DVRex will capture audio in that frequency (or in 32053hz per 
second if CanonAudio1=3 is not set), and convert the audio to 
48048hz and then create an AVI file in 48048hz. This will ease 
this noise somewhat.

Also during all this, an another setting was added to go around 
all the above settings. If you set Cap32to48=-1 in the ini file, 
all the above settings will become invalid, and DVRex will capture 
audio as is. But because RexEdit is set to output audio in 32032hz, 
if you use files that do not match this, the output will be out of sync.

Below is the current setting options in the canopus.ini for 
capturing audio. 

(no settings) - will look at the first second and measure the 
sampling rate, and if that sampling rate was outside the range 
of 32026hz to 32038hz, DVRex will consider the camera as an XL1 
and capture audio in 32053hz per second. After sampling as 32053hz 
per second, it will convert the audio to 48048hz, and then convert 
back to 32032hz, to create an AVI file. If the audio data is 
inside the range of 32026hz to 32038hz, DVRex will use the measured 
sampling rate and capture audio as that sampling rate, and create 
an AVI file.

CanonAudio1=3 - will look at the first second and measure the 
sampling rate, and DVRex will capture audio in that frequency. 
And if that sampling rate was outside the range of 32026hz to 
32038hz, DVRex will convert the audio to 48048hz, and then 
convert back to 32032hz, to create an AVI file. 

Cap32to48=1 - when the DVRex converts the audio to 48048hz, 
it will not convert it back to 32032hz and creates an AVI file 
in 48048hz.

Cap32to48=-1 - all the above settings will become invalid, and 
DVRex will capture audio as is. Output audio is set to 32032hz.


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1) Other cards
Sync: All 1394 capture cards that do not compensate for Canon XL-1 
audio irregularities (i.e. take the audio "as is") will go out of 
sync when making long caputures to NLE's. 
Distortion: They will, however, never have any distortion or audio 
degredation. (They may also be unreliable to use as my old DV300 card was.)

2) Canopus
Sync: Canopus wrote new code to compensate for the Canon XL-1 audio 
capture problems. When the card detects a problem, they resample 
the audio in proper format. As outlined in "Read This" this resampling 
can be manually disabled in the canopus.ini file. Unfortunately, there 
is a bug in the Raptor and the resampling cannot be disabled. For 
Canon GL-1 users, they want the resampling disabled, because on these 
cameras Canon basically corrected the problem, so they shouldn't be 
resampling. The fix for something that's not broken breaks it ;).

Distortion: Canopus's resampling routines seem to be primative. 
While it might not show when resampling 48.1kHz (Canon's error) to 
48.0kHz (the standard), it shows quite clearly in 32kHz audio. 
Why? Because the Canopus algorithm resamples 32 to 48 and back 
to 32. This is really bad news, and it introduces noise and 
distortion. If you know much about audio, you know that resampling 
is difficult, some call it a "black art". Most would never want 
their audio resampled, if possible. If you must resample, then 
you should use advanced coding like Sound Forge. Apparently, 
Canopus's resampling routine is flawed. Even if it wasn't, I would 
never recommend using it for optimum audio. Resampling audio is 
just a bad practice.

Solutions: For GL-1 users turn of the sampling ALWAYS by using 
cap32to48=-1 in the canopus.ini file. For XL-1 users, it's a trade 
off between audio resampling and long-term sync. I never capture 
long files, and I want the highest audio quality, so I'll turn my 
off all the time. For other XL-1 users, I would turn the audio 
resampling off for short captures. For long captures, I would use 
48kHz and leave the resampling on. 

Settings: Basically, the card resamples if it autodetects improperly 
sampled audio. To keep it on, do nothing. To turn it off use cap32to48=-1.

Raptor: The raptor has a bug which does not allow you to turn off 
resampling. For raptor users who want to turn it off, wait for the 
fix from canopus. For now it will always be on. When capturing using 
32kHz use cap32to48=1 to reduce the amount of distortion from 
resampling. This eliminates the last resampling routine in 32->48->32, 
and leaves you with 48kHz audio.

Good luck!
Charles