Re: [Sursound] Volume question WRT 7.1 sound recorded at listening position. (dw)
In years past, a number of systems has issues with intra-sample peaks. While a technical 0 dBFS cleared, the interpolated level between the peaks would cause distortion. From a best practices for broadcast point of view, my colleagues and I have just tried to steer clear of any overs, sample-wise or interpolated. We started working to -20 dBFS RMS as a matter of course. With the general move to 24 bit from 16 it's never presented any real issues. And as it happens, SMPTE has also recommended -20 dBFS as a nominal operation level as well! > On Sep 23, 2013, at 6:03 PM, Andy Furniss wrote: > > Ken Landers wrote: >> While -16.9 might keep you safe, a better option might be -20 dBFS. >> Gives some headroom in case you need it. Also, many consumer >> playback devices may not handle full scale output. > > Interesting, I am not a producer of anything as such, but do see that a > lot of digital music and some films push 0dBfs (though at least the > films aren't anywhere near RMS) > > Do you mean that consumer DACs can't handle it properly, or that the > analogue side doesn't being driven full voltage? > > Andy. > ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Volume question WRT 7.1 sound recorded at listening position.
On Mon, Sep 23, 2013 at 3:55 PM, Andy Furniss wrote: > > > I don't quite understand the "in phase" though, are you saying that they > artificially adjust phase for the same sound that comes out of more than > one speaker to affect the mixdown? The Recording Academy recommendations for surround sound say (sec 4.3) One potential problem that can arise from routing a signal into two or more speakers is the danger of increased, and increasingly complex, comb filtering. This problem multiplies as more speakers are engaged and can become critical if downmixing is ever employed by the playback system. Therefore, many experienced surround mixers selectively turn off channels when bringing a sound "inside" the surround bubble or when dynamically panning a sound from one area in the surround space to another. It is recommended that whenever signal is placed into three, four, or five speakers, it be decorrelated. http://www2.grammy.com/PDFs/Recording_Academy/Producers_And_Engineers/SurroundRecommendations.pdf -- Aaron (hel...@ai.sri.com) Menlo Park, CA US -- next part -- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20130923/a357f99b/attachment.html> ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Volume question WRT 7.1 sound recorded at listening position. (dw)
Ken Landers wrote: While -16.9 might keep you safe, a better option might be -20 dBFS. Gives some headroom in case you need it. Also, many consumer playback devices may not handle full scale output. Interesting, I am not a producer of anything as such, but do see that a lot of digital music and some films push 0dBfs (though at least the films aren't anywhere near RMS) Do you mean that consumer DACs can't handle it properly, or that the analogue side doesn't being driven full voltage? Andy. ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Volume question WRT 7.1 sound recorded at listening position.
dw wrote: On 22/09/2013 12:51, Andy Furniss wrote: Hi I do not have a 7.1 sound system so can't actually test this, also as may become apparent I don't know much about sound :-) I would be grateful if someone could correct/confirm the following. If I were to mix down a digital 7ch to mono I have to reduce by 1/7 amplitude to prevent clipping, so one channel will be -16.9dBfs. This assumes that all 7 channels are driven with the same maximum level, in phase, and that this would get past the mastering stage,, I'm sure they bear in mind the possibility of stereo, or mono mixdown. Yea I guess all channels full at once only really happens on the front three in practice, mine was just an example to make the figures as different as possible. I don't quite understand the "in phase" though, are you saying that they artificially adjust phase for the same sound that comes out of more than one speaker to affect the mixdown? Level wise, I don't think my method is any different from and software decoder, except of course various channels get different weighting before normalisation. Peaking at 0dbfs is evident on a couple of film soundtracks, disk and BBC broadcast I've just looked at (without compressing using the DRC metadata, of course). Of course in practice consumer 7.1 currently means TrueHD or DTS MA which seems to be mixed up rather than down - so there is a studio stereo mix there in the stream to be decoded directly. If I play the track over one speaker the volume difference between one and all channels will be 16.9dB. If I were to measure the volume at listening position (assuming anechoic and equal speaker distance) with a real 7 speaker setup then the volume difference, because the speakers are not close, would add up using power not amplitude so the difference heard/measured between 1 and 7 at full power would only be 8.45dB, so there is quite a large dynamic range discrepency? You would add powers if the 7 channels had random relative phase (which is less likely with "anechoic and equal speaker distance" Ok, so would infinite distance planewaves playing the same sound add as if the speakers were coupling (I thought you needed < 1/2 wavelength for this) to gain twice as much as power alone even though they are not in the same direction? Or is this a just a mathematical perfect position effect that wouldn't really happen in a real 7.1 setup even if the speakers were playing the same sound? The real reason for this question is more to do with simulation than real life, so perhaps that will make a difference - if the speakers are infinitely far producing planewaves and a soundfield is at listening position would that change anything for what levels the virtual omni would "hear". Sorry for all the questions - I would just like to understand if I use supercolliders 7.0 ambisonic encoder so I can then do either personal hrtf or uhj stereo decode, whether the simulation it uses is correct in the sense of the levels I would get with a real soundfield measuring real speakers. Thanks. Andy. ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] Volume question WRT 7.1 sound recorded at listening position. (dw)
While -16.9 might keep you safe, a better option might be -20 dBFS. Gives some headroom in case you need it. Also, many consumer playback devices may not handle full scale output. > On Sep 23, 2013, at 11:00 AM, sursound-requ...@music.vt.edu wrote: > > Send Sursound mailing list submissions to >sursound@music.vt.edu > > To subscribe or unsubscribe via the World Wide Web, visit >https://mail.music.vt.edu/mailman/listinfo/sursound > or, via email, send a message with subject or body 'help' to >sursound-requ...@music.vt.edu > > You can reach the person managing the list at >sursound-ow...@music.vt.edu > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Sursound digest..." > > > When replying, please remember to edit your Subject line to that of the > original message you are replying to, so it is more specific than "Re: > Contents of Sirsound-list digest..." so that it matches the post you are > replying to. > > Also, please EDIT the quoted post so that it is not the entire digest, but > just the post you are replying to. > > > Today's Topics: > > 1. Re: Volume question WRT 7.1 sound recorded at listening > position. (dw) > > > -- > > Message: 1 > Date: Sun, 22 Sep 2013 19:53:35 +0100 > From: dw > To: Surround Sound discussion group > Subject: Re: [Sursound] Volume question WRT 7.1 sound recorded at >listening position. > Message-ID: <523f3caf.4040...@dwareing.plus.com> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > >> On 22/09/2013 12:51, Andy Furniss wrote: >> Hi >> >> I do not have a 7.1 sound system so can't actually test this, also as >> may become apparent I don't know much about sound :-) >> >> I would be grateful if someone could correct/confirm the following. >> >> If I were to mix down a digital 7ch to mono I have to reduce by 1/7 >> amplitude to prevent clipping, so one channel will be -16.9dBfs. > This assumes that all 7 channels are driven with the same maximum level, > in phase, and that this would get past the mastering stage,, > I'm sure they bear in mind the possibility of stereo, or mono mixdown. >> >> If I play the track over one speaker the volume difference between one >> and all channels will be 16.9dB. >> >> If I were to measure the volume at listening position (assuming >> anechoic and equal speaker distance) with a real 7 speaker setup then >> the volume difference, because the speakers are not close, would add >> up using power not amplitude so the difference heard/measured between >> 1 and 7 at full power would only be 8.45dB, so there is quite a large >> dynamic range discrepency? > > You would add powers if the 7 channels had random relative phase (which > is less likely with "anechoic and equal speaker distance" > >> >> The real reason for this question is more to do with simulation than >> real life, so perhaps that will make a difference - if the speakers >> are infinitely far producing planewaves and a soundfield is at >> listening position would that change anything for what levels the >> virtual omni would "hear". >> >> TIA >> >> Andy. >> >> >> ___ >> Sursound mailing list >> Sursound@music.vt.edu >> https://mail.music.vt.edu/mailman/listinfo/sursound > > > > -- > > Subject: Digest Footer > > ___ > Sursound mailing list > Sursound@music.vt.edu > https://mail.music.vt.edu/mailman/listinfo/sursound > > > -- > > End of Sursound Digest, Vol 62, Issue 15 > > ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
Re: [Sursound] , ambi playback configution and calibration
Hi, Date: Thu, 19 Sep 2013 21:50:00 +0200 From: David Worrall To: Surround Sound discussion group Hi All, I'm away from my back-up of this list (*) so please forgive if this has been answered before, but Is there - on the market, or in other form - a setup system/tool that auto configures a decoder and calibrates an ambisonic playback rig according to the (actual) position of the loudspeakers? thanks, David Presumably it doesn't have to auto-locate the speakers ?? That would be clever and probably expensive. I have something that was built in MAX/MSP, and can turn it into an application (Mac OS preferred but Windows is probably possible). It is first order only, up to 16 speakers, and based on all the info about good decoders I've found, and can understand and implement. Of course it could be extended to higher orders, once the maths is thought through and the issue of different kinds of W. Haven't done this as most of the people I'm dealing with don't have enough speakers to make it worthwhile or essential. It's basically part of something else which is trying to do all sorts of ambisonic things with 16 inputs from a DAW running on the same computer. So, until higher powered computers become affordable in an income challenged age, processing power has to be carefully used. Increasing the ambisonic order starts to push up the number of audio streams that need handling in a non-linear manner. Such a decoder needs listening to, which means that you have to able to generate something to listen to to assess how well the encode/decode works, something I haven't had time to do above 2nd order. If only there was more time, things got done quicker, or someone was paying for the work by the hour. Ciao, Dave Hunt ___ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
