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Using a stereo amp for movies

Discussion in 'Home Cinema & Hi-Fi' started by TALON1973, 17 Apr 2020.

  1. lucid

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    Don't you just hate that when you do a copy and paste and it carries over the text formatting too. The text ends up either teeny-tiny or mahoosive. lol :D

    Now the speaker model confirmed, I'd definitely say that they're going to be the bottleneck on performance. It's not going to make much difference to the fidelity of the sound whether it's a good £330 stereo amp or a £300-£350 AV receiver. The speakers will flatten out most (if not all) of the amp benefits.

    If that's the case, I'd side with @hornetstinger and choose the convenience of an AV receiver.

    A Marantz NR-series might be a good bedroom AV receiver. They're half the height of traditional AV receivers, but still fully featured. The NR-1510 is 5.1, has optical and coaxial inputs plus 5x HDMI ins and an ARC/eARC HDMI out. That's good for future-proofing the compatibility with future TV upgrades. Front channel power is 50 W + 50 W (8 Ω/ohms, 20 Hz – 20 kHz with 0.08 % T.H.D.). That's pretty much the same measurement method as the Denon PMA-600ne, and the wattage is bloomin' close too. £369.
     
  2. TALON1973

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    Lol thanks lucid

    my other option is the denon pma-30. It would do me as an cheap option for 18 months. I can never stay in one sound option for long. I’d use the other speakers or sell them at some point.
     
  3. lucid

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    PMA-30 or PMA-600ne are just two sides of the same coin. Other than costing a bit less, and being a little more limited in the maximum volume it can drive, it doesn't change the game on the 2ch side.

    I still believe that a similarly-priced AV receiver will give you sound so similar you won't hear any appreciable difference, and that the receiver will outperform the stereo amp for convenience. This is, after all, primarily a TV viewing system. Your aim is to improve things over the Sonos Beam.

    You have more than enough information now to consider the pros and cons and make an informed choice.
     
  4. jpaul

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    getting an AV too, may give some EQ capabilities for the speakers
     
  5. lucid

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    That's a very valid point.
     
  6. hornetstinger

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    If it's not been mentioned already, with a stereo amp you'll lose .1 lfe content
     
  7. jpaul

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    I'd thought the denon he referenced did have a sub pre out, or you mean something else ?
    although, personally I'd sacrifice that, and don't have it, put the money into fuller range speakers ... at what frequency is the omni(cant' remember the term)directionality of base really significant.

    edit:
     
    Last edited: 23 Apr 2020
  8. hornetstinger

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    Sub out on a stereo amp doesn't mean the .1 lfe content.

    .1 lfe is dedicated signal that only DD/DTS processors decode. If you don't have that the .1 lfe content is lost.

    Sub out on a stereo amp is simply left and right audio summed into one signal output from a specific frequency it could be 80-120 typically.

    Bass becomes locatable at 120hz, at 60 or 80 it isn't

    Ideally for music I like it lowest as possible to where floorstander speakers trail off say 40-60hz
     
  9. jpaul

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    If the lfe has been mixed into the stereo 2.0 stream from freeview/blue-ray (per the quote I gave), then the stereo amp can filter them back out, to provide on the sub-out,
    that was my premise.
     
  10. hornetstinger

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    Nope. It's not included at decoder lecel
     
  11. lucid

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    @hornetstinger is correct. LFE is discarded in a multichannel-to-stereo down-mix.

    It's best practise to do this for two reasons. The first is because of phasing. LFE is mono, so splitting it across the left and right speaker channels can result in some odd effects of cancellation and reinforcement once the sound makes it out in to the room.

    The other reason is that the E in LFE stands for Effects.

    There's nothing in the studio mix of an LFE track that's essential to making a proper stereo mix. It doesn't carry voice or music or main channel surround info. The Low Frequency Effects channel carries additional bass up to 120Hz, but it is for effect only.

    The reasons for the existence of LFE aren't entirely straightforward. Some stuff is easy to grasp, such as the frequency limits of stereo and surround channels (20Hz-20kHz) which isn't low enough for all LFE content. Other stuff is more obscure such as the limits in what the optical track on 70mm cine film could cope with.

    One important point is that LFE doesn't equal subwoofer. That means losing the LFE track doesn't affect what the sub is doing for the main channel mix, or a sub working with a 5-channel-to-stereo mix.
     
  12. jpaul

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    I waited to see your opinon ... but at least this thread, I'd read following my post
    https://www.avsforum.com/forum/91-a...1482651-does-lfe-belong-stereo-downmix-3.html

    suggest that - indeed A DD/DTS decoder would take the LFE and optionally distribute it to a sub, and (seemed to contradict you)) front/rear speakers designated as LARGE,
    but that does not preclude 2.0pcm (pre-mixed) channels from set top boxes eg. freeview. having mixed(vestiges, is the word used) of LFE in their 2.0 PCM channel, so,
    the stereo amp (with sub out) would have it available,
    they would have to pre-mix it/LFE, in, at an appropriate level so it was not over-powering/destructive.

    [
    so ... I'm saying it's potentially icluded in the broadcast 2.0pcm (pre-)mix
    ]
     
  13. hornetstinger

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    No I'm saying lfe is included in post mix, maybe some avr do include lfe on stereo out. Guess depends on the unit, and setting.

    Guess only way to find out is to have a test disc with sole .1 lfe content and listen/feel what happens under different circumstances, ie a avr downmix, whether set to large or small, to stereo out, pre out, what happens with stereo amp, from sources, from sources like pc where have further options etc.
     
  14. hornetstinger

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    Safest option is to buy a avr.
     
  15. lucid

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    Not sure who you're replying to here. If it's me, then sorry, but I haven't time to wade through a page of AVS posts to find what you think is the relevant point. Maybe you should quote the text and the post number?

    However, looking at the rest of your post and it's reference to 2.0 from set top boxes, the very fact that it's 2.0 means it doesn't have an LFE track. That's what the .0 means; LFE track = 0 = no LFE.

    Also, what an AVR does with a 2.0 source has nothing to do with down mixing 5.1 to 2.0

    There isn't a 2.0 mix broadcast.

    The broadcast is in AAC 5.1 The box then converts to DD5.1 or pcm 2.0 depending on the capabilities of the sink device as reported via the EDID handshake or, in the case of an optical output, the menu settings for the box.
     
  16. jpaul

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    OK never mind - ... maybe what I said is so blindingly obvious

    bbc freeview mux are broadcast with several audio streams 2.0 aac and sometimes a 5.1, nowtv streamed is just 2.0

    when they prepare the 2.0 track they mix down the original 5.1, from a movie say, as you can do on a pc with ffmpeg command line example I showed

    they can mix the lfe track into the 2.0, in the same way that your own av can.

    since the lfe may be in the 2.0, it can be delievered to your stereo amp, which refutes the point hornetstinger had made
     
  17. hornetstinger

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    Only if you can demonstrate downmixed pcm has .1 lfe.and from reading, it is not included.

    It would make sense .1 is not discarded but it is


    Only way would be to try yourself, create a multi channel DD/dts track, with .1 lfe specific bass tones. Play that back on regular home theatre, you'll hear it. Play it back from downmixed TV to optical out, into a two channel. I'd it's not coming from anywhere then you know it's gone.

    Dolby spec says it's discarded.
     
  18. lucid

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    I'm sorry to say @jpaul, but your recent posts in this thread read to me largely as mad rambling. They seem to lack structure, and appear to be a sort of stream-of-consciousness outpouring of disjointed thoughts. Maybe what's in your head makes sense, but once it reaches the written page, it's not so clear. I'm trying to pick through the bones of them to make some sense, but it's not that easy. Perhaps you should proof-read and edit?

    The thread is about the pros and cons of a stereo amp versus an AV receiver. The speaker package will be run as 2.1 from the stereo amp because it has a sub out. However, this isn't the same kind of sub out as an AV receiver. It isn't managed in the same way. There's no crossover setting in the amp. The sub gets a full range audio signal. Full range for stereo equipment usually means 20Hz-20kHz. The sub's own volume, phase and crossover controls will blend the sub with the main speakers.

    One of the intended sources is a 4K player of some description. It's reasonable to presume then that the source is capable of delivering a 5.1 audio signal. From that, @hornetstinger made the valid point that when using a stereo amp would lose the .1 lfe content.

    Strictly speaking, the stereo amp wouldn't lose the signal as such because that would imply that it has received it in the first place, and that would be wrong. The .1 lfe would be discarded before it reaches the amp in the process of down-mixing a multichannel signal to stereo ready to be fed to a stereo amp.

    You're trying to argue that it wouldn't be discarded.

    It appears from what you've written that you seem to think that the way an AV receiver works with a 2.1 speaker package then somehow dictates how a stereo amp with a sub out socket should work. The way your posts read, you seem to be confusing the bass management of a stereo source signal with how lfe is handled.

    What happens with the bass from a 20Hz-20kHz main channel signal (a 2.0 signal, if you will), and how it is divided between the main speaker and the sub is nothing to do with lfe. There is no lfe content in a 2.0 source signal. The fact that a sub gets some bass signal fr4om an AV receiver doesn't mean that its an lfe signal. It's just bass. It's whatever is below the crossover-point set in the AV receiver's bass management controls.

    The fact that you can use some PC software to downmix a signal doesn't prove anything. By the way, your command line only appears to list the main surround channels. There's no part that appears to deal with lfe. Oopsie :o :o :o

    You've then banged on about broadcast audio streams - which I guess relative to you using the ffmpeg sofware.

    Freeview doesn't broadcast with a 5.1 and a 2.0 audio stream at the same time. It's wasteful of data bandwidth. There's no point either. Where the source film or TV program is in true 5.1 surround, but the TV or audio device requires a stereo signal, then it's the receiving device that is responsible for creating a stereo signal. It does this by using the 5.1 donor signal. In the process, anything in the .1 lfe channel is discarded.

    For a movie or TV program that was filmed and edited to be in stereo, then the broadcaster still uses the 5.1 framework, but only populates the channels relating to FL and FR. This means that centre, surround left, surround right and the lfe channels are empty of content. It's true then to say that the BBC has programming in 2.0 or 5.1, but a HD programme with 5.1 audio doesn't also have a 2.0 downmix broadcast at the same time. This goes some way to explaining why some people report incorrect audio flagging. The program is in stereo (usually with Dolby surround) but the receiving equipment reports it Dolby Digital after being transcoded from AAC-LE.
     
  19. jpaul

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    OK you've evidently understood my terse posts - honetstinger is super terse(verging enigmatic), the other end of spectrum., from yourself. !
    each to his own.


    Talon could elaborate, on, which would be the predominate source, but I'd speculate most viewing would be 2.0 sources,
    hence, I'd commented on whether LFE would really be lost.

    which is why I
    because they would be a predominate source.


    although, google, faster than writing the above, described how netflix prepare 2.0 audio stream, if i interpret it correctly
    which (since I only have 2.0 myself) 'comforts' me that I am not necessarily loosing out on lfe, like talon wouldn't be.
     
  20. lucid

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    @hornetstinger may be economical with his use of words, but what he writes usually makes sense even when he's arguing his point passionately. Do you see the difference?


    It doesn't really matter. The question is what happens when bits of hardware in the system that @TALON1973 would run convert 5.1 to 2.0 Any source stream that is already 2.0 will pass unchanged.

    Here's the problem with just Googling some key phrases and then using them to substantiate your position in a technical discussion: You have to understand their context. I'll take your Netflix example.

    Firstly, this isn't how Netflix prepares anything. Look at the title of the document. It's an instruction to the programme makers on how to deliver content. There's an important difference.

    Secondly, this is an instruction to mixing engineers. It includes words to the effect of 'check it for errors before you deliver your programme to us". That's very different from what happens with an on-the-fly hardware conversion of 5.1 to 2.0 in domestic gear.

    If you had a mixing engineer sat in your lounge, and you were prepared to wait for that person to remix all your 5.1 content, then check it for phasing errors and, if necessary, reprocess it with additional tools to iron out those bumps, then sure, you could have LFE retained.

    The thing is that none of that is practical.in the real world where a bit of silicon does an on-the-fly down-conversion. Discarding LFE for all the reasons I have previously outlined is the safest option. You can choose to disagree; that's your right.