- Joined
- Feb 23, 2016
- Messages
- 20,766
- Likes
- 37,625
I measured the Focusrite Forte recording interface. In this case focusing on the DAC. This was a nice two channel recording interface which has been discontinued. The ADC and DAC chips and much of the circuitry is what is used in the current Focusrite Clarett line of interfaces. It has two microphone inputs with up to 75 db of gain which is higher than usual. Also line level and instrument inputs (for guitars). Headphone, and monitor outputs. It is a 24bit/192 khz ADC/DAC. The Forte has a Display Port dongle for some connections and a touchscreen for many of the controls. It connects via USB using ASIO in windows and Focusrite software in Mac. It sold for most of its life around the $450 to 400 mark.
The measurement FFTs are all 32K FFTs as is the custom on ASR. The spectrograms used a 2k FFT. As is Amir's custom I'll start with a 12 khz -1 db tone. Very tight central spike and not much else. Ignore the little blip at 16.3 khz as that shows up when my ADC is connected to my Macbook Pro. BTW, the ADC used for measurements is the Antelope Audio Zen Tour.
Here is the 0-300 hz spectrum while producing the 12 khz tone. I think you'll agree it is pretty clean.
A combined chart showing a - 60 db 1 khz tone and the full 12 khz tone to show the noise floor is not modulated by the signal. Most DACs do modulate that just a little and some more than a little. AES17 Dynamic range is 114 db.
The ubiquitous 1 khz thd plot. 2nd harmonic is below -120 db and the 3rd is about -106 db. You see some fifth and a little 9th for some reason. SINAD is 104 db.
Here is a twin tone IMD plot with -6db tones at 18 khz and 19 khz. The 1 khz difference signal is -120 db. While the first sidebands around the main tones lie around -100 db. Not too bad I don't think.
I like to look at spectrograms because you can spot other spurious signals, aliasing, imaging etc. very easily. I use 2 k FFTs for this as it catches even short lived blips or glitches. In the following you see a single max level tone sweep from 2hz-20khz. Next to it is a two tone sweep at max level. The tones are a constant 1 khz apart. I have it set so at -100 db the background goes to medium gray.
In this case there is very nearly nothing from these tones above the -100 dbFS level. A little IMD creeps in just under that at the upper most frequencies.
Next the same thing except I have the background going to medium gray at -120 db. So anything above that level will show in the graph. You can see some harmonic distortion showing up at these levels. Also a touch of imaging in the upper 2 khz. You also see the 16.3 khz idle tone of the ADC in these graphs. If your monitor is good you can see a tiny hint of the 1 khz difference tone in the IMD side of the spectrogram.
Though not shown linearity is good to 20 bits. I didn't test lower, it probably is good even lower than this.
The measurement FFTs are all 32K FFTs as is the custom on ASR. The spectrograms used a 2k FFT. As is Amir's custom I'll start with a 12 khz -1 db tone. Very tight central spike and not much else. Ignore the little blip at 16.3 khz as that shows up when my ADC is connected to my Macbook Pro. BTW, the ADC used for measurements is the Antelope Audio Zen Tour.
Here is the 0-300 hz spectrum while producing the 12 khz tone. I think you'll agree it is pretty clean.
A combined chart showing a - 60 db 1 khz tone and the full 12 khz tone to show the noise floor is not modulated by the signal. Most DACs do modulate that just a little and some more than a little. AES17 Dynamic range is 114 db.
The ubiquitous 1 khz thd plot. 2nd harmonic is below -120 db and the 3rd is about -106 db. You see some fifth and a little 9th for some reason. SINAD is 104 db.
Here is a twin tone IMD plot with -6db tones at 18 khz and 19 khz. The 1 khz difference signal is -120 db. While the first sidebands around the main tones lie around -100 db. Not too bad I don't think.
I like to look at spectrograms because you can spot other spurious signals, aliasing, imaging etc. very easily. I use 2 k FFTs for this as it catches even short lived blips or glitches. In the following you see a single max level tone sweep from 2hz-20khz. Next to it is a two tone sweep at max level. The tones are a constant 1 khz apart. I have it set so at -100 db the background goes to medium gray.
In this case there is very nearly nothing from these tones above the -100 dbFS level. A little IMD creeps in just under that at the upper most frequencies.
Next the same thing except I have the background going to medium gray at -120 db. So anything above that level will show in the graph. You can see some harmonic distortion showing up at these levels. Also a touch of imaging in the upper 2 khz. You also see the 16.3 khz idle tone of the ADC in these graphs. If your monitor is good you can see a tiny hint of the 1 khz difference tone in the IMD side of the spectrogram.
Though not shown linearity is good to 20 bits. I didn't test lower, it probably is good even lower than this.
Attachments
Last edited: