- Qiao Jianzhong 喬建中 and Wu Guodong 伍國棟 (eds), Zheshan chang nashan 這山唱那山 [English title Polyphonic folksongs in China] (2-CD set, 2002), with booklet in Chinese.
It makes an important addition to our roster of folk polyphony around the world—best known on the world-music scene through the recordings of Le Mystère des Voix Bulgares. For guidance on multi-part singing we may also consult the CD-set Voices of the world and its instructive booklet.
The cultures of China’s ethnic minorities are a popular topic—  more so, indeed, than those of the Han Chinese, thanks largely to the reductive image of ethnic groups being “good at singing and dancing”, and their exotic costumes.
All this is well beyond my expertise, but since the 1980s, along with research, there’s a substantial repository of audio and video recordings, and minority groups are commonly invited to give staged performances in urban festivals. The vocal repertoires of many such peoples include a substantial component of polyphonic songs. 
The two CDs contain 56 tracks—mostly a cappella—from 16 ethnic groups in provinces such as Yunnan, Guizhou, and Sichuan, including Buyi [Bouyei], Miao [Hmong], Jingpo, Yi, Naxi [Nakhi], Lisu, Dong [Kam], Zhuang (16 tracks!), Yao, Molao, Maonan, Bai, and Qiang, as well as Tibetans and Mongols, and the She minority of Fujian in the southeast.
Most of the recordings were made (in concert, rather than in situ) at a major gathering of singing groups for a 1982 symposium in Nanning—just as the liberalisations that followed the collapse of the commune system were allowing traditional culture to revive, but rather before migration, tourism, commodification, and heritagification further thickened the plot.
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Many other recordings of the musics of ethnic minorities are the result of “hit-and-run” missions. But for the poor mountainous province of Yunnan, the long-term studies of local fieldworkers Zhang Xingrong and Li Wei, often in collaboration with British ethnomusicologist Helen Rees, are most diligent. Their numerous CDs include both ritual and instrumental genres and vocal music. For the latter, most relevant here are
- Alili: multi-part folksongs of Yunnan’s ethnic minorities (2 CDs, Pan, 2004) and the sequel Nanwoka (2 CDs, Pan, 2005),
with field and studio recordings (again mostly a cappella, with only occasional instrumental accompaniment) of the Yi, Hani, Nakhi, Lisu, Nu, Lahu, Jinuo, Jingpo, Tibetans (9 tracks), Bai, Miao, Yao, Zhuang, Bouyei, Dai, Wa, De’ang, Bulang, Achang, and Dulong peoples—both sets containing most instructive liner notes. Here’s the playlist of the former (click on “YouTube”):
Particularly remarkable are the multi-part songs of the Hani (only “discovered” in 1995)— such as the densely-textured clusters of this rice-transplanting song (well documented in the liner notes):
- the CD Baishibai: songs of the minority nationalities of Yunnan (Pan, 1995, playlist here)
- the 2-DVD set From China’s southwest borders: minority dances, songs and instrumental music of Yunnan (2001)
- and, covering all the diverse expressive genres, the compendium
Zhang Xingrong 张兴荣 (ed.), Sanjiang bingliu quyu yinyue wenhua daguan 三江并流区域音乐文化大观 [English title Musical cultures of the Three Parallel Rivers region of Yunnan] (2012), comprising a richly-illustrated 574-page book, 4 DVDs, and 2 CDs! 
Simply as pure sound (whatever that is), all these CDs are ear-opening, often mesmerising—remote from the commodified versions of “folk-song” common in the media. Of course, as I never tire of saying, audio recordings tend to reify; there’s no substitute for observing musicking in all its messy social context—including migration, tourism, and so on. Though online videos tend to be highly idealised, under the guidance of Xiao Mei at the Centre for Ritual Music Studies at the Shanghai Conservatoire, some more thoughtful ethnographic documentaries are being made.
While one can hardly expect the long history of the accommodation of these groups with state power to intrude into such accounts, for the interplay of ritual and politics among the Yi people in Yunnan under Maoism and since, do read Erik Mueggler, The age of wild ghosts.
All this just to remind myself why I don’t dare venture into the field of the ethnic minorities…
 In Chinese, a useful diachronic survey of PRC research on minority musics is Du Yaxiong 杜亚雄, “Ershishiji Zhongguo shaoshu minzu yinyue fazhan zhi huigu” 二十世纪中国少数民族音乐发展之回顾 (2000). The ethnic minorities of Taiwan are also much studied.
 In Chinese, a standard textbook on multi-part singing is Fan Zuyin, Zhongguo duoshengbu min’ge gailun 中国多声部民歌概论 (1994).
 For the whole project (quite separate from the Anthology for Yunnan), note Helen Rees, “From field recordings to ethnographically informed CDs: curating the sounds of Yunnan for a niche foreign market”, in Levi S. Gibbs (ed.), Faces of tradition in Chinese performing arts (2020). An evocative introduction to the work of Zhang Xingrong is the interview in CHIME 8 (1995) by Jack Body—another avid fieldworker in the region during the period. For further detail on the Hani songs, with transcription, see Zhang Xingrong, “A new discovery: traditional 8-part polyphonic singing of the Hani of Yunnan”, CHIME 10/11 (1997). For the Kam/Dong people in Guizhou (another highly popular topic), the publications of Catherine Ingram are detailed and nuanced. An ambitious ongoing series of CDs of China’s ethnic minority songs is reviewed here.