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Radically upgrade your sound and music experience with this 100dB HiFi Bluetooth speaker/portable audio monitor. 50 hours playtime!
1,083 backers pledged £84,768 to help bring this project to life.

Our decision about AptX

Posted by Frankenspiel Ltd. (Creator)

Hi everyone,

We've received requests to consider adding AptX support to the FS-X specification. 

The reasons put forward for this have been:
- it would add to the audio quality of the FS-X 
- it would make for better stereo audio 
- it would add to its Sales appeal, "ticking boxes".

We realise that it's an important issue for some of you - let's not mince words, a deal breaker in fact - while for others it would be a "nice to have". It's for that reason we have taken time to re evaluate the issue thoroughly. Thank you for your patience, while we carried out this review.

Here we summarise our findings, for those who want more detail, see the White Paper on audio quality in FS-X below.

1. We understand that Apt-X is being implemented more and more in newer smartphones. It is however, e.g. not supported by any Apple mobile device. AptX is a proprietory codec, this would mean that FS-X would offer a different audio experience to those with or without AptX support in their devices.

2. Given the approach we have taken to the design and implementation of the audio in FS-X - where each stage and component of the whole audio path is kept to the highest performance - incorporating AptX would force a re-design of the whole audio path, and it wouldn’t yield any improvement.

3. Incorporating AptX would as far as we are informed, mean that we would have to abandon one of our crucial design goals - namely, true wireless stereo.

What is true wireless stereo and why is it important?
From a single device like a smartphone (or tablet), you can link to two speakers (one left and one right) through Bluetooth without any wires and you’re free to place the speakers wherever you wish. The two speakers behave like true stereo left and right channels. And as such they are synchronised.

While with FS-X the mono experience is great, loud enough to fill a room, with two FS-Xs, the sound separation of stereo brings more detail and richness (as well as more dB), adding enormously to the sound experience.

Think of it this way, if you install a classic stereo speaker system, you would never dream of putting the two speakers right next to each other, let alone in the same box. So we believe, so should it be with wireless. Forgive the pun, but is this truly, “thinking outside the box”.

If we adopt AptX we would be forced into a re-design, which would add time and cost but not any extra audio benefit, and it would mean putting left and right speakers in a single box. This is not what our backers have pledged for and we're not prepared to do this.

So, in Frankenspiel’s modular approach, by just pairing with your smartphone (or tablet), you can create a HiFi true left/right wireless stereo sound system.

Our design philosophy begins with the idea that (practically) everyone has Bluetooth audio. We then tried to design a speaker that does exactly what people want. FS-X sounds good not because the design ticks boxes, but because it's based on a careful analysis of each stage (the whole audio path) and making sure we use the very best architecture and components to reach our goal.  

White PaperFS-X Bluetooth Audio   

Modular Wireless Stereo System

While due to its bandwidth limitations, Bluetooth cannot wirelessly transmit the same uncompressed CD quality audio as wire, Bluetooth IS capable of transmitting higher bitrate lossy files. If the rest of the audio path of the speaker is properly and carefully designed, (as it is in the FS-X), the music experience will be virtually indistinguishable from CD across wire.

What Frankenspiel is introducing with FS-X is Modular Wireless Stereo. You can buy one speaker or more, each is a complete system. If you choose you can pick up one speaker and it will give you a great wireless or wired sound experience. Use it as a portable speaker, take it on your bike, or on a hike, in the bathroom or the kitchen. It has the battery life to go with a “take anywhere” attitude. You can also use it wired. If you want stereo you add a second unit and it will give you TRUE wireless stereo.

While with FS-X the mono (stereo down-mix) experience is great, loud enough to fill a room, with some sound stage separation induced by DSP, with two FS-Xs, the sound separation of stereo brings more detail and richness (as well as more dB), adding enormously to the sound experience.

Think of it this way, if you install a classic stereo speaker system, you would never dream of putting the two speakers right next to each other, let alone in the same box. We believe, it should be exactly the same for Bluetooth wireless. Forgive the pun, but this truly is “thinking outside the box”.

So, in Frankenspiel’s modular approach, by just pairing with your smartphone (or tablet), you can create a HiFi true left/right stereo sound system, where you are free to place the two speakers wherever you wish completely without wires. Or, if you wish you have a great portable mono speaker or audio monitor fitting in the palm of your hand.

Making the FS-X able to support true stereo wireless over Bluetooth is no easy challenge, (for a start left and right channels have to be perfectly synchronised). But we believe it yields benefits beyond just the audio aspects. You can start with a single speaker: if you choose you can add another later, knowing that the two will work together as true stereo.

For a discussion of file types and audio quality see the note below.

Speaker Design and Bluetooth Audio

The user audio experience from a wireless bluetooth speaker depends on a number of factors:
- the wireless link
- the digital analog conversion
- pre-amp stage
- power amplifier stage
- transducer

Each of these stages present opportunities to optimise the final user experience, or potential pitfalls which could render the final user experience disappointing.

The wireless transmission:
Under the A2DP Bluetooth Audio profile, the mandated SBC codec is capable of being set at a high enough bitrate to match higher bitrate lossy files. For example in “High Quality” mode (@328kbit/s) it is on a par with ATRAC SP (Type-R, @292kbit/s) compression algorithm which is used in Minidisc recorders/players. Recordings made on these, are generally considered to be HiFi by most demanding listeners.

But after you have transmitted the bits over using the SBC Codec, there are many other issues which the selection of audio codec has no influence or control over. After all the codec itself is a tiny part of the overall audio chain.

To get the most out of what is a barely acceptable audio codec, it needs to be made part of perfectly designed audio circuits with component parts carefully matched. If this is not done, the result is poor audio, and for this Bluetooth cannot be blamed.

In other words, the potential for Bluetooth audio is there but it needs to be fully exploited through good (audio) design.

The other side of this coin, is that the potential for poor audio design is enormous.

If DAC conversion, or amplification, is done at low quality, if there is an error in digital-analog conversion, if the amp or driver is low quality, any one of these can lead to poor audio quality - even if the audio codec is in “high quality” mode. Proprietory extensions to the Codec will be unable to “compensate” for failure to ensure that every single phase of the audio path is optimised sufficiently.

With FS-X, Frankenspiel’s approach is different: the whole audio path is kept to the highest performance - no room for conversion errors - and care is taken to use (matched) high spec components, e.g. the audio chain input from Bluetooth feeds directly into the amplifier, and above all, the quality of the transducer is outstanding.

It is this approach that enables us to guarantee high audio quality when rendering wireless audio through FS-X via standard Bluetooth audio.

Analog (cabled) operation:A final word on analog - the analog line-in on FS-X is 24bit ADC (note: this is the same quality as a FLAC file), so quality is maintained throughout.


Note on file types and audio quality:

This is outside the control of the speaker designer, but is crucial - what you transmit counts.

Bluetooth audio codecs can handle lossy files. But there is a world of difference between an MP3 file created using the setting of 128 kbps which will have a compression ratio of 11:1 and lossy files such as AAC @ 320 kbps which have compression ratio of around 4:1.

Playing 128 kbps you will encounter audible problems, vocals will be muddy, missing details, clarity of some instruments is lost and bass loses its original power. Playing 320 kbps files, on the the other hand you have the chance that (provided the whole audio chain is well implemented) the listening experience will be close to indistinguishable from CD files over wire.

Amazon and iTunes offers 256kbps, Spotify’s premium service is at 320 kbps and most new YouTube material is now encoded to 320 kbps.


We've done our best to make this as concise and complete as possible. 
Please feel free to comment on this. 

Best regards,

The Frankenspiel Team

Jeff, Alex Zak, and 7 more people like this update.


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    1. Frankenspiel Ltd. Creator on

      @ Magsy: You write “AptX in no way effects stereo operation”, this is true as long as you’re prepared to accept left and right driver co-located in a single box, or left and right channel wired together. But we’re after a stereo solution which moves beyond this to true wireless stereo.
      The discussion of AptX has always been in the context of Standard AptX. Not AptX Lossless or AptX Low Latency.
      In answer to your last comment: we hope that our White Paper makes clear what we’re trying to achieve with true wireless stereo and why we’re not able to implement AptX and maintain our design goals.

    2. Frankenspiel Ltd. Creator on

      @ Jon Webb & ben1680: Thanks for your comments.

    3. Frankenspiel Ltd. Creator on

      @ Ruben Adriaanse: Thanks! We prefer to use the standard SBC codec. You can play FLAC files through the FS-X.

    4. Missing avatar

      Magsy on

      You have largely dodged the issue rather than directly address it. Stereo has been around forever and is not part of this discussion. AptX in no way effects stereo operation.

      Having cherry picked parts of an article easily found on Google, you should have at least credited the source. SBC cannot be compared to MP3 or AAC, it is less efficient low complexity codec based on a very different encoding principal (because these devices are very low powered)

      The codec is not a small part of the chain....garbage in garbage out, see the success of something like Pono; people are starting to care and this is the first step. To be clear I do not expect high end, large speaker audiophile sound, however why hobble it at the first step in the chain?

      If we are placing such high importance on the other parts of the chain, what is the DAC?

      Stereo is supported by the other AptX speakers, Hidden Radio 2 for example. Bluetooth does support lossless; via AptX.

      I guess the answer to Aptx is that it is outside your control and too difficult; fine, you should have just said that.

    5. ben1680

      @Creator Thanks for your care in explaining this issue in detail.

    6. ben1680

      The sound quality difference might not be apparent to some people, but I'm not that lucky. With the good source material, I can pick the difference between the normal Bluetooth and AptX, even with small speaker with good driver.

    7. Jon Webb on

      In my experience, AptX doesn't deserve all the hype it is getting. I'm fine with A2DP with a high bitrate.

    8. Missing avatar

      Ruben on

      Great to hear that high quality is more important than ticking boxes. Under the A2DP there is mandatory support for the SBC codec, but others (even manufacturer-defined codecs, such as aptX) can be added. So why not add a lossless codec like FLAC? Kleer has already done this right? Maybe I'm confusing a couple things but hopefully you will be able to tweak the final touches to make the best product possible!

    9. Frankenspiel Ltd. Creator on

      @ JB: Thanks! :)

    10. Frankenspiel Ltd. Creator on

      @ Oliver: Sorry to have kept you waiting! The update on the add-ons (Update #13) is finally out!

    11. JB on

      Epic comment!

    12. Missing avatar

      Oliver Schöpfer on

      Hey guys how can i get the case and the fast charger too? I allready purchased the the 2 speakers.