46.875kHz sample rate? EP-133, Others? History Matters?

elvish_paisley 🎙️ · 3 weeks ago

Hi All,

I hope this is the right forum. Apologies if this is just a little random.

A while ago I had sampler GAS and noticed the Teenage Engineering EP-133 had the “odd” sample rate of 46.875kHz. It seemed like it might be annoying for file transfers and I never really figured out why it was used.

I just noticed my Line 6 Filter Pro also uses the “odd” sample rate of 46.875kHz. I’m not sure it’s relevant to anything, but again I was curious where it came from and why.

Regarding the EP-133 I found the following information.
https://news.ycombinator.com/item?id=38379543

Code:

It might be because of the clock of the CPU or the dac being 24Mhz.
24MHz/512=46.875KHz
Edit: or 12, 6, 3...
  24MHz/512=46.875KHz
  12MHz/256=46.875KHz
  6MHz/128=46.875KHz
  3MHz/64=46.875KHz...
also
I've heard Lexicon used to use weird sample rates in its reverbs to make it harder to reverse engineer.

The real explanation seems to be here.
https://www.audiosciencereview.com/f...ing-rate.4309/

Code:

93.75kHz and 46.875kHz are the sampling frequencies Bruno Putzeys uses in all his digital products for Hypex, Grimm audio, KII, etc.

Here is the reasoning, taken from the LS1 white paper:

    5.2 Clock
    The clock circuit is the same as that used in the CC1
    except that the sampling rate is set to 93.75kHz instead
    of one of the more traditional audio rates. This is specifically
    done to improve the performance of the SRC chip.
    An uncommon clock frequency reduces the odds that mix
    products between the incoming clock and the internal
    clock fall inside the PLL loop bandwidth of the SRC.

Looking for other devices that use 46.875kHz I stumbled on this comment in this thread, though it notes “Not much use to people really but I went digging...”
Another reverb thread
Behringer Virtualizer 3D FX2000
Behringer Virtualizer DSP1000P V2
Behringer Virtualizer Pro DSP2024P

I stumbled on this interesting, kinda recent (2024), article about the 1986 Acorn BBC Micro 500 digital synthesizer, whose digital oscillators had a “max sample rate: 46.875Khz per channel(!)”. I guess this only refers to the digital-to-analog conversion?
https://sonicstate.com/news/2024/02/...0-synthesizer/

It appears 46.875kHz is also the highest sample rate for CD that is compatible with European video formats? https://en.wikipedia.org/wiki/PCM_adaptor

Anyway, as near as I can tell this “odd” sample rate comes from squeezing the highest audio quality out of chips that can’t do 48k. At this point it’s an indicator of cheaper/slower/older chips? It’s otherwise not important, right? Is it worth listing other devices that use 46.875kHz?

Cheers!
Elvish

ShadowsOfLife · 3 weeks ago

Quote:

Originally Posted by elvish_paisley ➡️

Hi All,

I hope this is the right forum. Apologies if this is just a little random.

A while ago I had sampler GAS and noticed the Teenage Engineering EP-133 had the “odd” sample rate of 46.875kHz. It seemed like it might be annoying for file transfers and I never really figured out why it was used.

I just noticed my Line 6 Filter Pro also uses the “odd” sample rate of 46.875kHz. I’m not sure it’s relevant to anything, but again I was curious where it came from and why.

Regarding the EP-133 I found the following information.
https://news.ycombinator.com/item?id=38379543

Code:

It might be because of the clock of the CPU or the dac being 24Mhz.
24MHz/512=46.875KHz
Edit: or 12, 6, 3...
  24MHz/512=46.875KHz
  12MHz/256=46.875KHz
  6MHz/128=46.875KHz
  3MHz/64=46.875KHz...
also
I've heard Lexicon used to use weird sample rates in its reverbs to make it harder to reverse engineer.

The real explanation seems to be here.
https://www.audiosciencereview.com/f...ing-rate.4309/

Code:

93.75kHz and 46.875kHz are the sampling frequencies Bruno Putzeys uses in all his digital products for Hypex, Grimm audio, KII, etc.

Here is the reasoning, taken from the LS1 white paper:

    5.2 Clock
    The clock circuit is the same as that used in the CC1
    except that the sampling rate is set to 93.75kHz instead
    of one of the more traditional audio rates. This is specifically
    done to improve the performance of the SRC chip.
    An uncommon clock frequency reduces the odds that mix
    products between the incoming clock and the internal
    clock fall inside the PLL loop bandwidth of the SRC.

Looking for other devices that use 46.875kHz I stumbled on this comment in this thread, though it notes “Not much use to people really but I went digging...”
Another reverb thread
Behringer Virtualizer 3D FX2000
Behringer Virtualizer DSP1000P V2
Behringer Virtualizer Pro DSP2024P

I stumbled on this interesting, kinda recent (2024), article about the 1986 Acorn BBC Micro 500 digital synthesizer, whose digital oscillators had a “max sample rate: 46.875Khz per channel(!)”. I guess this only refers to the digital-to-analog conversion?
https://sonicstate.com/news/2024/02/...0-synthesizer/

It appears 46.875kHz is also the highest sample rate for CD that is compatible with European video formats? https://en.wikipedia.org/wiki/PCM_adaptor

Anyway, as near as I can tell this “odd” sample rate comes from squeezing the highest audio quality out of chips that can’t do 48k. At this point it’s an indicator of cheaper/slower/older chips? It’s otherwise not important, right? Is it worth listing other devices that use 46.875kHz?

Cheers!
Elvish

I don't know about this sample rate being used to "squeeze the highest audio quality out of chips that can't do 48K". You'll certainly get more high-frequency audio with a higher sample rate, but it's still above what anyone can hear. And while you could get away with a filter that's not as steep as the ones used for dedicated 44.1 kHz devices, I'm not seeing any "audiophile"-level manufacturers using this sample rate. (Behringer isn't exactly an audiophile-level manufacturer.) And of course, "highest quality audio" implies money spent on all parts of the DAC.

As far as what the 1986 Acorn BBC Micro 500 used, that article on SonicState.com was penned by our own @ Xpanderbeanz — someone who definitely knows gear and how to get the most out of even "lo-fi" gear that others dismiss. Maybe we'll get some more info on that...?

Steve

ShadowsOfLife · 3 weeks ago

Forgot to mention...thanks for the link to that article. I was aware of SonicState.com, but not those articles. I'll probably spend the rest of the afternoon reading them and watching the videos.

Steve

elvish_paisley 🎙️ · 2 weeks ago

Quote:

Originally Posted by ShadowsOfLife ➡️

I don't know about this sample rate being used to "squeeze the highest audio quality out of chips that can't do 48K". You'll certainly get more high-frequency audio with a higher sample rate, but it's still above what anyone can hear. And while you could get away with a filter that's not as steep as the ones used for dedicated 44.1 kHz devices, I'm not seeing any "audiophile"-level manufacturers using this sample rate. (Behringer isn't exactly an audiophile-level manufacturer.) And of course, "highest quality audio" implies money spent on all parts of the DAC.

As far as what the 1986 Acorn BBC Micro 500 used, that article on SonicState.com was penned by our own @ Xpanderbeanz — someone who definitely knows gear and how to get the most out of even "lo-fi" gear that others dismiss. Maybe we'll get some more info on that...?

Steve

Thanks for the reply.

I suppose I should have been more careful about the language I used. I didn't mean to imply 46.875kHz was "high quality" or even good. I guess I was thinking it might be better than 44.1kHz, or maybe it's just an attempt by manufacturers to advertise a bigger number.

Thanks for pointing out the author on that SonicState.com article, I missed that. I'm a fan too, already subscribed to their YouTube channel.

Quote:

Originally Posted by ShadowsOfLife ➡️

Forgot to mention...thanks for the link to that article. I was aware of SonicState.com, but not those articles. I'll probably spend the rest of the afternoon reading them and watching the videos.

Steve

Ya, that article was my favorite part of this random research journey. Looked up the bitshifters on SoundCloud and found some other Acorn 500 music. I take a look at more of those articles too. I'm curious if you find anything interesting.

Cheers,
Alex

ShadowsOfLife · 2 weeks ago

Quote:

Originally Posted by elvish_paisley ➡️

Thanks for the reply.

I suppose I should have been more careful about the language I used. I didn't mean to imply 46.875kHz was "high quality" or even good. I guess I was thinking it might be better than 44.1kHz, or maybe it's just an attempt by manufacturers to advertise a bigger number.

Thanks for pointing out the author on that SonicState.com article, I missed that. I'm a fan too, already subscribed to their YouTube channel.

Ya, that article was my favorite part of this random research journey. Looked up the bitshifters on SoundCloud and found some other Acorn 500 music. I take a look at more of those articles too. I'm curious if you find anything interesting.

Cheers,
Alex

I've allocated 40 minutes today to read the articles and watch the videos or listen to the SoundCloud links.

I've already accepted that 90 minutes into this I'll admit that 40 minutes was never going to be enough time...so I'll just go for two full hours.

Steve

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