De-jittering with iFi S/PDIF iPurifier for Spotify

Continuing from my last post on my music exploration with Spotify (here), I continued to think about what other tweaks I could try out to improve Spotify's MP3-equivalent sound quality. 

I thought about jitter, which we audiophiles have learned is one of the big influencers in digital music replay quality. So I decided to search for a de-jittering device, something like the Ultra Jitterbug from Sonic Frontiers or the Genesis Digital Lens of yore, to see whether it would make any difference to Spotify's sound quality feeding my TAD-D600's DAC.  

Again, I didn't want to spend too much money, not knowing a de-jittering device's efficacy on the TAD-D600, given that TAD has paid special attention to the D600's master clock to reduce jitter with a proprietary high precision crystal oscillator. 

After some research online, I turned up with the iFi S/PDIF iPurifier (there is also a iPurifier version for USB), which iFi says does its work in 4 stages - " isolation, regeneration, a memory buffer and re-clocking. This restores the industry standard ‘square wave’ which represents the desired signal". The iFi S/PDIF iPurifier can also convert between coaxial and optical input/output too. I don't want to get into its technical specifications too much, you can read more on iFi's website.

Again, I found a used one online, it is a S/PDIF iPurifier version 1 (list price USD150). iFi has come out with iPurifier 2 which performs the same functions as far as I could ascertain. 

My need is the iPurifier's coaxial connection. For this, the iPurifier has a female RCA on one end, which the digital data feed from my Bluetooth receiver will go into, and a male RCA on the other end, which will be plugged into the digital input on the TAD-D600.

The iPurifier comes with a wall wart power supply that converts our AC into 5v DC which iFi says is a low noise power supply. I ran the iPurifier with this wall wart for a start. In no time I could hear the iPurifier's contribution to the sound quality. Basically, the improvements came in terms of improved precision, with a clearer sound and slightly heightened resolution at both ends of the frequency spectrum. The images became more focused with better definition in the bass and treble regions. 

With prolonged listening, despite these improvements, I felt that that was a certain hash in the sound that I didn't like. So I got myself another battery pack to supply 5v DC to the iPurifier, just like I did with the Bluetooth receiver as in my last post. That did the trick, the sound became smoother overall.  

Here are 2 recordings used to compare the effects without and with the iFi S/PDIF iPurifier in the loop. Noted that resolution wise they are at Spotify highest quality setting which is 320kb/s, less than a quarter of the CD's 1,411kb/s, so we can't expect miracle here. These recordings were done with an iPhone SE, hand held. The sound quality differences may be difficult to hear on mobile devices' or a PC's built in speakers, a pair of good headphones should do better. 

1. "Historia De Un Amor" by Lisa Ono, on her album "Romance Latino Selection" 

1a. Without iFi iPurifier

1b. With iFi iPurifier

The effects I noticed may be deemed subtle, but they are there. I found that the decay of each piano note cleaner with the iPurifier, There is also a similar effect with Ono's breathiness and decay at the end of each phrase of her vocal part. Each musical note, including the bass notes are also rendered with better definition. The brushed cymbal (from 1:32 onwards) stands out a little more with better dynamic shading, though its resolution is limited by the bitrate.

I prefer the sound with the iPurifier, but I can understand too if some listeners preferred the slightly warmer and looser sound without.

2. "Imperial March" - John Williams and Vienna Philharmonic from "John Williams in Vienna"

Listen to the entire track and compare how each one holds your listening attention more from beginning to end.

2a. Without iFi iPurifier

2b. With iFi iPurifier

To me, this example is all about rhythm and momentum. The recording with the iPurifier holds the musical line tighter and propels the music along better, with the music sounding more relentless and more urgent, as it should be.

Lastly, just sharing a track that a reader requested. Nice song. I just played it from Spotify and recorded it with the same setup:

3. "It Knows Me" - Avi Kaplan

Putting on the audiophile hat, I think in this recording there is a tilt in the balance towards the bottom end, it is bass heavy. With the resolution level offered by Spotify, the bass part is dense rather than well defined. The situation is further exacerbated by a somewhat recessed vocal. This track can be a challenge to a system with too much bass to play it in a well balanced manner in my view. 

Final thought - ya, in HiFi, little things do add up. The tweaks I did improved Spotify's replay to a level that is more palatable to me, which is a good thing - Spotify has become a staple in my HiFi system for me to explore new music. 

1. Spotify for my Hi-Fi / 2. SMPS vs Battery

1. Spotify for my Hi-Fi

My family has subscribed to Spotify Premium for a while. The kids love it for its convenience, huge selection, and user friendliness. For me, as Spotify does not offer CD-quality or hi-res music, I have been using it to check out new music or for casual listening on my handphone. 

But, I have this nagging feeling, I was itching to know how Spotify's lossy music files would sound on my Hi-Fi rig (Spotify uses the Ogg Vorbis codec, which is similar to MP3). I know they won't sound close to CD/SACD quality, but if they sounded just ok I'd have even more music to play. 

I decided to experiment. Not sure of the outcome, I resolved to keep things simple, keep the cost down and make use of what I already have. 

I already have a DAC. My TAD-D600 CD//SACD player comes with digital inputs, and I know the quality of its DAC section is formidable. The digital inputs are AES/EBU (XLR) and S/PDIF (coaxial only, no optical). They accept up to 24bit/196kHz. Spotify's bitrate is not even close, so no problem there (gentle reminder to Spotify Premium subscribers - set "music quality" in your Settings to "Very high", that will give you the highest bitrate of 320kb/s). 

Next was how to get the bits into the TAD-D600. I wanted a simple and low cost option. I thought the most straightforward solution was to go through the Bluetooth route, where I could stream the signal wirelessly from my handphone or my notebook PC. Bluetooth's transmission protocol can handle Spotify's 320kb/s bitrate without loss (sure, there are many other higher quality solution than Bluetooth that I could explore of course, that will be for another time).

So, my requirement was to get a Bluetooth receiver sans DAC that would output at least a S/PDIF signal via a RCA jack. The obvious thing was to search online for it. It turned out that there are many choices for Bluetooth with S/PDIF optical output, but one with RCA was not so common. I found one eventually for slightly over RM100 (~USD25) from where else but China. 

The no-name Bluetooth receiver with digital out

The Bluetooth receiver takes a 5v DC power input via a mini USB jack, so any phone charger would suffice. I used one from my iPad. 

For the digital cable I dug up my old van den Hul The First interconnect cable that also doubled up quite well as a digital cable. 

I didn't have a high expectation of the sound quality. I just wanted to be able to listen to music, to explore, via my Hi-Fi rig. With the bar set low, the results surprised me actually. I could not only listen to music but actually enjoy it a lot too. 

The Bluetooth feed going into the coaxial digital input of the TAD-D600 player

From the audiophile's point of view, I can say these from my listening experience with Spotify played via a HiFi rig:

- The sound is relatively warm - so most of the time it is a nice and comfortable listen. Just put on one's music-enjoyment mode and put the sound-analysis mode behind. That is to put it positively. To be more critical, the sound is rolled off at the top though not to the point of making the music sound dark, the lower mid and the bass region is also somewhat blurry and lacking resolution (thus the perception of  warmness in the music). 

- Playing simpler and quieter music is very acceptable and quite enjoyable (folk, vocal accompanied with a few instruments, small ensembles). Not quite so with complex music (such as big symphonies, dynamic sound tracks, or hard rock), and not when one wishes to push the volume higher. The sound would fall apart, getting somewhat disorganized, and rough around the edges when faced with these challenges. It is like there aren't enough "bits" to go around to construct the music.

- Dynamic range and transient attack is somewhat compressed compared to what I am used to from CDs. This is not an entirely bad thing, simpler music would do more than fine, sounding sweet and relaxed.

- There is soundstage and imaging, though on a smaller scale and less sharply done than with CDs, but it is there. Separation and layering are quite acceptable too.  

Here are a few clips of my system playing streams from Spotify. The video recordings were done on an iPhone SE 2020, handheld (so pardon the not-so-stable video), no other equipment was used.

1. Anne-Sophie Mutter and John Williams - "Rey's Theme - From "Star Wars: The Force Awakens" - from the album "Across The Stars". Track 1

2. Mendeleyev, a "The Voice" contestant, doing a cover version of Bob Dylan's "Girl from The North Country"

3. Regina Spektor - "The Call". 

If not for my daughter's Spotify playlist, I would not have discovered this song - this thing is really letting me discover new music already. 

Streaming Spotify is not going to replace my main CD music diet, that is for sure. Some say 320kbit/s is close enough or even similar to CD's sound quality, I respectfully disagree, it is just not so with my own experience, especially when listening at more realistic level. However Spotify has open up a great new dimension for music exploration. I have gone on to buy the CD version of albums that I heard and liked on Spotify. 

After a few days, just like any audiophile, I started to think what tweaks I could try, to see whether the sound quality could be improved upon. 

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2. SMPS vs Battery

I mentioned that I used an iPad charger to supply 5V DC to the Bluetooth receiver right? Just like any other phone charger it is of the SMPS (switch-mode power supply) type. We read a lot in the Hi-Fi press that an SMPS is noisy and an LPS (linear power supply) is better for sound quality anytime. 

But an LPS can be expensive, some go into the 4-figure region, which kinda violates the rule I set for myself - simple and cheap. So my mind turned to battery - don't we also read that battery power supply is quiet and good, even better than LPS in some applications? 

Initially I thought of using a handphone powerbank for this purpose. It worked, but the powerbank shut itself down automatically after a few minutes of use. I think its internal circuit sensed that it was not connected to a handphone that is being charged, though the Bluetooth receiver is actually drawing power from it. 

So I turned to online shopping again. I found a power supply originally meant for bicycle LED light. It takes 4 AA batteries and has a USB output, just the thing for the Bluetooth receiver. Cost? Less than RM20 (~USD5) shipped from China. 

I was a little surprised when I plugged the Bluetooth receiver into the battery power supply. The sound quality did improve, but it was not about the background noise or the sound becoming quieter, which was the effect I expected from battery vs SMPS. 

Rather, the rolled off highs took on a bit more extension and clarity, the lower mid and bass region gained a bit more definition. Dynamic and attack were better, and this opened up the sound further. The roughness and feeling of disorganization with complex music or when played loud was reduced. 

Not night and day differences, but not bad for such a low cost and simple option. 

Not sure how well you can hear these differences from a phone recording. Anyway, here goes, the same music as previously, with the preamp volume set at the same level as before.

4. Anne-Sophie Mutter and John Williams - "Rey's Theme - From "Star Wars: The Force Awakens" - from the album "Across The Stars". Track 1 - Recording 2 with battery power supply on the Bluetooth receiver

With the battery supply on the Bluetooth receiver, there is a bit more shimmering in the violin tone, and greater extension in the higher registers. The sound is a little more dynamic, it holds the listener's attention better. It is more exciting to listen to overall, pay attention to the points where the music shifts gear around 0:31, 1:38 and 2:05.

 

5. Mendeleyev, doing a cover version of Bob Dylan's "Girl from The North Country" - Recording 2 with battery power supply on the Bluetooth receiver 

The strumming on the guitar is more emphatic and has better attack. The guitar is also brought more in line with the vocal, whereas previously the guitar tone is relatively more subdued. Mendeleyev's vocal also shows more nuances. 

 

I am happy with these results and has been exploring new music, though the MP3 level sound quality is nowhere close to CD (but of course). We audiophiles do not know when to leave well enough alone, I started thinking again about what else to do to improve the sound quality from Spotify further. Well, that's for the next write-up.