[LAU] Sound quality of the Focusrite Scarlett 18i20 2nd Gen

[Ralf Mardorf]

Hi Tom,

thank you for reporting your experiences. Until now I only tested the
outputs. Not only the headphone outputs sound bad, the analog line
outputs sound disgusting, too. The sound is comparable to turning on
Dolby B on a cheap tape recorder, without pumping, but with cutting
highs and in addition with boosting bass or like having dirt in the ear
or having hearing issues caused by a cold. All analog outputs are
unusable crap. The companies claim that it's a professional device is a
lie, it's even not a home recording or cheap hifi device.

I experienced a new issue, that might be an issue for all USB devices on
my machine. I didn't do that much tests with the Presonus as I already
did with the Focusrite. A few times Qtractor as well as Ardour had
issues to read WAV data from the hard disk. Fortunately Ardour informs
about the reason, Qtractor doesn't. One time I needed to restart the
computer to get rid of it. I tested two SATA HDDs, so it's seemingly
not a broken HDD, but most likely an issue related to USB.

It seems not to be related to an IRQ...

[rocketmouse at archlinux ~]$ rtirq status

  PID CLS RTPRIO  NI PRI %CPU STAT COMMAND	
  126 FF      90   - 130  0.2 S    irq/19-ehci_hcd	
  130 FF      90   - 130  0.0 S    irq/16-ohci_hcd	
  152 FF      89   - 129  0.0 S    irq/17-ohci_hcd	
  154 FF      88   - 128  0.0 S    irq/18-ohci_hcd	
  155 FF      88   - 128  0.0 S    irq/17-ohci_hcd	
  157 FF      87   - 127  0.0 S    irq/18-ohci_hcd	
  274 FF      85   - 125  0.0 S    irq/18-snd_hdsp	
   32 FF      50   -  90  0.0 S    irq/9-acpi	
   48 FF      50   -  90  0.0 S    irq/8-rtc0	
   78 FF      50   -  90  0.0 S    irq/26-radeon	
  115 FF      50   -  90  0.0 S    irq/1-i8042	
  129 FF      50   -  90  0.0 S    irq/22-firewire	
  132 FF      50   -  90  0.0 S    irq/22-ahci[000	
  142 FF      50   -  90  0.0 S    irq/14-pata_ati	
  143 FF      50   -  90  0.0 S    irq/15-pata_ati	
  261 FF      50   -  90  0.0 S    irq/7-parport0	
  436 FF      50   -  90  0.0 S    irq/27-enp3s0	
    3 TS       -   0  19  0.0 S    ksoftirqd/0	
   17 TS       -   0  19  0.0 S    ksoftirqd/1

...ahci doesn't share its IRQ with USB. However, I'll continue with
some fine tuning.

[rocketmouse at archlinux ~]$ sudo modprobe -r pata_atiixp
[rocketmouse at archlinux ~]$ sudo modprobe -r firewire-ohci; sudo modprobe -r firewire_core
[rocketmouse at archlinux ~]$ sudo modprobe -r ppdev; sudo modprobe -r lp
[rocketmouse at archlinux ~]$ cd /sys/bus/pci/drivers/ohci-pci
[rocketmouse at archlinux ohci-pci]$ printf "0000:00:13.2" | sudo tee unbind >/dev/null
[rocketmouse at archlinux ohci-pci]$ printf "0000:00:13.4" | sudo tee unbind >/dev/null
[rocketmouse at archlinux ohci-pci]$ rtirq status

  PID CLS RTPRIO  NI PRI %CPU STAT COMMAND	
  126 FF      90   - 130  0.2 S    irq/19-ehci_hcd	
  130 FF      90   - 130  0.0 S    irq/16-ohci_hcd	
  152 FF      89   - 129  0.0 S    irq/17-ohci_hcd	
  155 FF      88   - 128  0.0 S    irq/17-ohci_hcd	
  274 FF      85   - 125  0.0 S    irq/18-snd_hdsp	
   32 FF      50   -  90  0.0 S    irq/9-acpi	
   48 FF      50   -  90  0.0 S    irq/8-rtc0	
   78 FF      50   -  90  0.0 S    irq/26-radeon	
  115 FF      50   -  90  0.0 S    irq/1-i8042	
  132 FF      50   -  90  0.0 S    irq/22-ahci[000	
  261 FF      50   -  90  0.0 S    irq/7-parport0	
  436 FF      50   -  90  0.0 S    irq/27-enp3s0	
    3 TS       -   0  19  0.0 S    ksoftirqd/0	
   17 TS       -   0  19  0.0 S    ksoftirqd/1

The Presonus and Focusrite cost < 400 EUR, alternatively there are just
2 Behringer for < 300 EUR and 1 RME for > 600 EUR.

I don't test the Behringer devices, because I read customer reviews
mentioning power supply failures for one of those devices and I had to
replace caps of my Behringer mixer's switching power supply and the
power supply of my ADA8000 gets boiling hot. I guess the only reason
that the ADA's power supply didn't break is, that I rarely used it.
Apart from this I had to clean all knobs of my Behringer mixing
console. I'm living close to a main street and dirt is a serious issue,
however, all of my gear suffers from the same dirt, but just the
Behringer mixer needed a radical cleaning in a shorter space of time.

The RME is too expensive. If all ADAT channels of my RME HDSPe AIO of
my Linux PC would work, I would buy and test the RME USB audio
interface, but because they don't, there's a Linux driver issue or I'm
to stupid to understand how to use it, I need to buy two devices, one
for the iPad and a second for the Linux PC, so the RME interface is too
expensive for me at the moment.

I continue testing the Focusrite now, assuming there should be no
additional issues, at least no issues for the iPad, I'll stay with the
Focusrite and use it for MIDI and ADAT. I still need to test the
analog inputs, perhaps they are usable. I also will call my dealer, too
ensure that the output sound isn't bad, because something is broken.

The analog outputs of the RME HDSPe AIO and the Behringer ADA8000 do not
sound that bad, so it's not some technical issue with my PC, mixer, amp
or ears. The culprits are the analog outputs of the Focusrite. My two
TerraTec EWX 24/96 cards aren't mounted, but I'm sure that even those
cards don't sound that bad, especially since even my cheap hifi CD
player does sound better, than the Focusrite. The headphone amp of the
Presonus wasn't very good, but it didn't colour the sound that much and
unfavourable as the Focusrite does. Unfortunately I didn't test the
sound quality of the Presonus outputs.

Regards,
Ralf