But I have been thinking about it -- fatal!
If you start off from WXY, which is what I use, and make these into
4.0, you have merely done a linear transform (a sophisticated LR-->SD
relationship). As this is totally lossless, any added phase anomalies
either before or after the transform, while they may not give the
same effect, could be significant. All I can say is that I have not
heard any significant degradation of my recordings when coding them
into high rate MP4 and playing them over the internet before
subsequent decoding.
I am not trying to be awkward, just trying to make sense of this!
David
At 13:12 25-10-17, Dave Malham wrote:
>I should have said "storing pre-decoded signals in a compressed format has
>less potential to be problematic" since phase errors likely to upset
>pre-decoded material would probably also cause problems with stereo which
>hopefully would have been picked up and dealt with during testing. I should
>say here that that's just what I feel likely to be the case, I can't say
>that I've actually tested it.
>
> Dave
>
>On 25 October 2017 at 11:30, David Pickett <d...@fugato.com> wrote:
>
>> At 09:55 25-10-17, Dave Malham wrote:
>>
>> > Just a word of warning, take care using compressed formats like mp4 for
>> >storing B format. If the compression used is lossy, this can screw up the
>> >decoding since phase errors can result in the sum and difference equations
>> >involved producing wrong results. Of course, storing pre-decoded signals
>> in
>> >a compressed format doesn't suffer from this.
>>
>> Dave,
>>
>> I always add add shelf filtering and then decode from B format to 4.0
>> before encoding to MP4. I dont see why there should not also be phase
>> problems with encoding 4.0 signals in MP4 (why do you say not?); but I have
>> never noticed any.
>>
>> David
>>
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>
>
>
>--
>
>As of 1st October 2012, I have retired from the University.
>
>These are my own views and may or may not be shared by the University
>
>Dave Malham
>Honorary Fellow, Department of Music
>The University of York
>York YO10 5DD
>UK
>
>'Ambisonics - Component Imaging for Audio'
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