[sdiy] Decent 192kHz USB audio-interface

[Jimmy Moore]

Do let us know what you end up deciding on (and why!). It may help someone
looking to branch into adjacent areas.

On Sun, May 2, 2021 at 9:40 AM Richie Burnett <rburnett at richieburnett.co.uk>
wrote:

> Hi guys and girls,
>
> Thanks for all your suggestions with this on and off the list.  Some
> manufacturer's names are cropping up again and again.  Definitely got some
> good leads to look into.
>
> -Richie,
>
>
>
> -----Original Message-----
> From: Mike Bryant
> Sent: Friday, April 30, 2021 10:40 AM
> To: Brian Willoughby
> Cc: synth-diy mailing list
> Subject: Re: [sdiy] Decent 192kHz USB audio-interface
>
> > "Then drops like a stone" seems to imply a brick wall filter. Aren't
> those
> > expensive in analog implementations?
>
> Not really - the combination of capacitors on the input transistor bases,
> then on the feedback of every op-amp, then the final RC feeding the ADC
> are
> all set to around 80-100kHz in most designs so as to make sure there's no
> response at the bottom of the long-wave radio band.
>
> Just realised that the hyper-expensive AK4558 has a very extended
> frequency
> response in the slow roll-off mode so add that to the list, not that it's
> available at the moment due to the AKM fab fire.
>
> There's also quite a few 384kHz devices available now, though some seem to
> start a slow roll-off at around 48kHz.  Still plenty of response at 80kHz
> but definitely not flat.
>
>
> -----Original Message-----
> From: Brian Willoughby [mailto:brianw at audiobanshee.com]
> Sent: 30 April 2021 01:58
> To: Mike Bryant
> Cc: synth-diy mailing list
> Subject: Re: [sdiy] Decent 192kHz USB audio-interface
>
> Thanks, Mike.
>
> "Then drops like a stone" seems to imply a brick wall filter. Aren't those
> expensive in analog implementations?
>
> On that note, if the AFE has a brick wall at 80 kHz, then it's not really
> relying on the ADC for the frequency response - at least the ADC isn't
> going
> to be able to be set to 384 kHz sample rate and change the frequency
> response much in that regard.
>
> ... not that we're talking about 384 kHz sampling - that would be crazy
> talk.
>
> Brian
>
> p.s. I'll mention that the Metric Halo Labs interfaces have DC response on
> the line level input path to the ADC. They don't maintain DC response on
> the
> mic preamp settings because of phantom power and other aspects of the
> microphone preamp stage. The Owners' Manual specifies a response of 1.8 Hz
> to 64.7 kHz +0/-1.0dB @ fs = 192 kHz. If you want tighter frequency
> response, it's 5.7 Hz to 42.1 kHz +0/-0.1dB at the same sample rate.
> 0.0005%
> THD @ -12 dBFS, 0.0015% THD @ -0 dBFS. I'm not sure which chips they're
> using, but it might be the AK4395.
>
>
> On Apr 29, 2021, at 17:15, Mike Bryant wrote:
> > Every mic preamp ADC I know of, including several I've designed myself
> > which I won't plug here, primarily rely on the ADC itself to set the
> > frequency response.  The AFE usually has a 3dB point of around 80kHz or
> > higher so as not to affect the overall phase response, then drops like a
> > stone to avoid any RF getting to the ADC.
> >
> > Also AKM and Cirrus ADCs seem to stick to a 40kHz bandwidth at 192kHz
> > sampling so it may only be ESS or custom equipped units that can do
> 80kHz.
> >
> > On Thu, Apr 29, 2021 at 6:19 PM Mike Bryant wrote:
> >>
> >> Most high frequency sampling ADCs aren't good to 80kHz.  They have a
> much
> >> more relaxed roll-off to about 40kHz to avoid phase effects on the
> audio,
> >> then dive.  Probably best to look at the ADCs datasheets from AKM,
> Cirrus
> >> and Analog Devices and find an ADC that does what you want, then look
> for
> >> units that use that device.
> >>
> >> -----Original Message-----
> >> From: Richie Burnett
> >> Sent: 29 April 2021 11:44
> >>
> >> Can anyone recommend a decent external USB audio interface that's
> capable
> >> of sampling at 192kHz in record and playback?
> >>
> >> This is a bit off topic, but it's still audio related! ;-)  Some of my
> >> colleagues do underwater acoustic communications work and have been
> using
> >> a "Creative Labs Sound Blaster X-Fi HD 24-bit 96KHz USB Audio
> Interface"
> >> with great success to record and playback ultrasonic signals up to
> 44kHz.
> >> Now they are wanting to do similar up to around 80kHz so I'm looking
> for
> >> an external audio interface capable of sampling at 192kHz with an
> >> analogue bandwidth out to around 80kHz.
> >>
> >> The only application I'm aware of that requires this sort of analogue
> >> bandwidth is the delivery of composite FM stereo multiplex from studio
> to
> >> transmitter site over IP.  So, I know it is possible, but wanted to
> avoid
> >> buying lots of audio interfaces and testing them to see which are good
> to
> >> 80kHz!
> >>
> >> Any tips/pointers/experience good or bad would be much appreciated.
> >> Off-list is fine if high-bandwidth audio is not considered to be of
> >> interest to others.
> >>
> >> Many thanks in advance,
> >>
> >> -Richie,
>
>
>
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