What does the M Scaler actually do, and is it worth adding to my DAC?
Short answer
Watts describes an M Scaler as an external interpolation filter that replaces the front-end filter inside your DAC, and in a podcast recorded in October 2025 (published March 2026) said Chord DACs from a Mojo to a Dave all benefit ecoustics 24:23. He calls it essential for his own listening Head-Fi, Jul 2022The Source AV 15:39, but says some people hear little, especially with less transparent amps or speakers Head-Fi, Nov 2018The Source AV 17:36. Whether it is worth the cost, he wrote in 2019, you can only find out by listening Head-Fi, Dec 2019.
Practical answer. Rob Watts describes an M Scaler (the Hugo M Scaler, or the larger Quartet first shown in 2024) as an outboard filter: "when you're adding a scaler, you're replacing the front end digital interpolation filter that's built into the DAC" ecoustics 24:23. He said DACs from a Mojo to a Dave "all benefit" (podcast recorded October 2025) ecoustics 24:23. For himself it is essential Head-Fi, Jul 2022The Source AV 15:39. On value, he wrote in 2019 that what remains is whether you can hear the difference "and whether the difference is worth the cost to you", which only listening settles Head-Fi, Dec 2019.
What he says it does
Every DAC upsamples, he wrote in 2019, so "the real question to ask is not whether a DAC upsamples, but how well it does the upsampling" Head-Fi, Dec 2019. The M scaler filter (identical code in the Blu 2 and the Hugo M Scaler Head-Fi, Aug 2018) uses 1M taps whose coefficients match an ideal sinc function to better than 16 bits; he gave 16.6 bits in March and July 2018 Head-Fi, Mar 2018Head-Fi, Jul 2018 and 16.7 bits in October 2018 Head-Fi, Oct 2018. It turns 44.1 kHz into 705.6 kHz and 48 kHz into 768 kHz, and "converting the 44.1 kHz to 705.6 kHz is not adding any more information" Head-Fi, Aug 2018. On Hugo 2 and Qutest, he wrote in February 2018, the DAC's first WTA filter stage is bypassed when an M scaler is connected Head-Fi, Feb 2018.
His stated reason it matters is transient timing: conventional filters make transients slightly early or late, and the brain uses transients to perceive pitch, timbre and soundstage Head-Fi, Aug 2018Head-Fi, Jul 2018.
By product
- Dave: in January 2018 he said you hear an M scaler on Dave "within 3 seconds" Head-Fi, Jan 2018. He wrote that Quartet "lifts Dave into a whole new realm" (May 2024) Head-Fi, May 2024 and said in an interview published March 2026 (recording date not stated) that it takes Dave "to a completely new level" Audio Force 19:17.
- Hugo 2 and Qutest: in March 2018 he wrote that they "benefit enormously by using an M scaler" Head-Fi, Mar 2018; in September 2018, that "an M scaled Dave easily beats an M scaled Qutest" Head-Fi, Sep 2018. Hugo 2 connects via 3.5mm to RCA cables plus BNC adaptors (July 2018) Head-Fi, Jul 2018. In October 2024 he said he uses Quartet with a Hugo 2 when traveling Head-Fi, Oct 2024.
- Hugo TT 2: advising a TT2 owner in November 2018, he said the occasions when the M scaler was "not a huge difference" involved "not very transparent amps and speakers", not a TT2 driving LCD-4s, and suggested a week of listening, then a day in pass-through Head-Fi, Nov 2018.
- Mojo 2: in September 2023 he wrote "you will get better sound quality if you use an M scaler on Mojo 2" Head-Fi, Sep 2023. In July 2023 he said Mojo 2 and Hugo 2 accept the dual data connection Head-Fi, Jul 2023, and in May 2024 that Quartet can be used with a Mojo 2 ConvinceMeAudio 11:42.
- Original Mojo: in January 2020 he wrote that dual BNC input was dropped from the original Mojo to save power; it takes 768k on USB and 384k on coax Head-Fi, Jan 2020.
- Non-Chord DACs: in January 2017 he wrote that Dave gets the maximum benefit, though with other DACs "clearly you will hear an improvement" Head-Fi, Jan 2017. In that podcast (published March 2026) he said the Hugo M Scaler's 192 kHz output "will feed any DAC", but "you only get the real benefit when you run it seven six eight" ecoustics 25:10.
- Quartet versus Hugo M Scaler: in April 2024 he said Quartet "will work with all current DACs" Head-Fi, Apr 2024. In June 2024 he called it "a major advance on Hugo M scaler" that "does everything that HMS does but more so", while the Hugo M Scaler stayed "absolutely essential" for him on flights Head-Fi, Jun 2024. In an interview published August 2026 (recording date not stated) he called Quartet "an expensive scaler" The Source AV 4:30.
When you may hear little
In September 2025 he said some people hear little while others find it essential, and that he has demoed Quartet and the M Scaler where "you can barely hear a difference because your system is not transparent" The Source AV 16:52The Source AV 17:36. In December 2018 he named "questionable headphones or loudspeakers" and stress during A/B tests Head-Fi, Dec 2018. In an interview published October 2026 (recording date not stated; its transcript places it before May 2026) he named Class D power amplifiers and poor loudspeakers or amplifiers HiFi Buys 2:24:19.
Setup notes he gave
For the Hugo M Scaler he recommended 75 ohm BNC cable (August 2018) Head-Fi, Aug 2018 and the supplied power supply over a linear one (September 2018) Head-Fi, Sep 2018; for Quartet, only the supplied power supply (January 2025) Head-Fi, Jan 2025. He said never to feed up-sampled signals into his DACs, "even a Mojo" (March 2018), and repeated it for Mojo 2 in 2023 Head-Fi, Mar 2018Head-Fi, Sep 2023.
What he has not said
Beyond leaving value to the listener Head-Fi, Dec 2019, he gives no value-for-money verdict, and no test for a transparent enough system beyond the examples above.
Quotes
“converting the 44.1 kHz to 705.6 kHz is not adding any more information”2018-08-02 Head-Fi, Aug 2018
“the M scaler is not an upgrade - it's transformational, in that you get that master tape feeling, or being in touch with the musical performance.”2018-07-24 Head-Fi, Jul 2018
“to me the M scaler is absolutely essential for good sound quality and for musicality.”2022-07-14 Head-Fi, Jul 2022
“some people try it and say, I can't hear much of a difference. And then some people, like myself, they try it and they say it's absolutely 100% essential.”2025-09-14 The Source AV 16:52
Dated positions
| When | Products | Position |
|---|---|---|
| 2017-01 to 2018-07 | DAVE, Blu Mk2, Hugo M Scaler | He said he had not expected the M scaler to be transformational, then described it as transformational and essential for his own listening; in January 2017 he said Dave gets the maximum benefit and he was unsure how much other DACs would gain. Head-Fi, Jan 2017Head-Fi, Jan 2017Head-Fi, Jul 2018 |
| 2018-02 to 2018-11 | Hugo 2, Qutest, Hugo TT2, DAVE, Hugo M Scaler | He said Hugo 2 and Qutest benefit enormously from an M scaler, that an M scaled Dave still beats an M scaled Qutest, and that the few occasions of little difference involved less transparent amps and speakers. Head-Fi, Mar 2018Head-Fi, Sep 2018Head-Fi, Nov 2018 |
| 2020-01 | Mojo (original) | He said dual BNC input was dropped from the original Mojo; it accepts 768k on USB and 384k on coax. Head-Fi, Jan 2020 |
| 2022-07 to 2023-09 | Hugo M Scaler, DAVE, Mojo 2, Hugo 2 | He said the M scaler is absolutely essential to him, that Mojo 2 and Hugo 2 accept the dual data connection, and that an M scaler improves Mojo 2. Head-Fi, Jul 2022Head-Fi, Jul 2023Head-Fi, Sep 2023 |
| 2024-04 to 2024-10 | Quartet M Scaler, Hugo M Scaler, DAVE, Mojo 2, Hugo 2 | He said Quartet works with all current DACs including Mojo 2, was designed to match Dave, and is a major advance on the Hugo M Scaler, which he still called essential on flights. Head-Fi, Apr 2024ConvinceMeAudio 11:42HIFICLUBE.NET JVH 8Head-Fi, Jun 2024Head-Fi, Oct 2024 |
| 2025-09 to 2026-10 | Hugo M Scaler, Quartet M Scaler, Mojo (original), Mojo 2, DAVE | He said he always uses the M Scaler when listening, that DACs from Mojo to Dave all benefit, and that people with non-transparent systems or Class D amplifiers may hear little. The Source AV 15:39ecoustics 24:23The Source AV 17:36HiFi Buys 2:24:19 |
Caveats and open points
- Watts gives no value-for-money verdict; in 2019 he left that to the listener, and his price remarks on Quartet are that it would cost more than Dave (May 2024, pre-launch) and is expensive (interview published August 2026).
- The 'from a Mojo to a Dave' remark (October 2025 podcast) does not say which Mojo; in 2020 he wrote that the original Mojo lacks dual BNC input.
- Most 2017 to 2019 statements concern the Blu 2 or Hugo M Scaler; Quartet statements date from 2024 onward and are not interchangeable.
- Head-Fi, Jul 2018 (July 2018) and Head-Fi, Nov 2018 (November 2018) carry dates estimated from their post IDs, as does Head-Fi, Jul 2018 (July 2018); the date shown for Head-Fi, Jul 2018 in the quotations above is that estimate.
Topics: Why upscale, and why a separate scaler, Pairing a scaler with a DAC, Tap length and diminishing returns